Delaware Reef Club

Why Make Your Own Rock?
The first mention I heard of Diy rock was in 2004 on www.3reef.com and it mentioned the use of different materials to make cheap rock. There was little information and even fewer had tried it. Most felt it was a way to beat the high price of live rock and that’s what initially drove me to it. While doing research on the new tank I was building, I decided I wanted to take as little from the ocean as possible. This Diy rock was the way to go. With the little information I found I made the first batch. Quite a bit has changed as aquarists have plenty of places to get info today.  Reef Central and GARF have threads and postings on making Diy rocks however the most exotic displays are found on www.cichlid-forum.com. This article is not an original work but a compilation of what I have read and the trial and errors I have made with my own rock. I included links at the end of this article but special thanks goes to InsaneReefer's thread on RC.

Getting people to make there own live rock will reduce the burden on the diminishing natural reefs. The goal of using rock whether live or Diy is for coral display and to have a healthy and thriving population of bacteria sponges and micro fauna. Diy Rock does not work exactly like live rock does. Live rock has the benefit of boring worms and algae that have over millions of years transformed the rock to have many small cavities and capillaries for micro fauna and bacteria to colonize. Diy rock will achieve an aerobic and anerobic area because of the porosity of concrete. Over time, the depth that this process of de-nitrification will occur will increase as the presence of worms and sponges dig into the rock, but it starts right on the outer surface to a depth of ¼ inch. As for the long-term success or failure of concrete in the aquarium; public aquariums have relied on it for their displays for 30 plus years.

Concrete is an ideal solid support, which can be prepared in shapes very similar to the randomness of existing reefs. Concrete, either in fabricated units specifically designed for artificial reefs or imperfect concrete manufactured products, such as culvert or rubble from razed buildings, sidewalks, roadways and bridges, has a demonstrated high success rate as artificial reef material in both marine and estuarine environments. The obvious reason for this high rate of success is the strong compatibility of the material with the environment in which it is placed. Concrete is generally very durable and stable as artificial reef material. Portland cement is largely made from lime, a component of limestone. Limestone is comprised primarily of calcium carbonate, which is the substance of which coral reefs are made. Since 1995 concrete culvert has aided in the restoration of the Delaware Bay. There are currently 50 patch reefs spread across 8 estuarine reef sites. Concrete reefs in Delaware support tautog and provide habitat for sea bass along with an epifaunal community dominated by polychaete worms. The are companies that specialize in concrete reef repair. Reef Balls uses their concrete to rebuild damaged reefs through their Reef Restoration projects all over the world.

Although the terms cement and concrete often are used interchangeably, cement is actually an ingredient of concrete. Concrete is basically a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and portland cement. portland cement is not a brand name, but the generic term for the type of cement used in virtually all concrete. Cement comprises from 10 to 15 percent of the concrete mix, by volume. Through a process called hydration, the cement and water produce crystals that interlock and bind the aggregates into a rocklike mass. This hardening process continues for years meaning that concrete gets stronger as it gets older. Hydration happens rapidly at first and slows down as time goes by. To measure the ultimate strength of concrete would require a wait of several years. This would be impractical, so a time period of 28 days was selected by specification writing authorities as the age that all concrete should be tested. At this age, a substantial percentage of the hydration has taken place. Concrete if made correctly and allowed to cure properly can last 50,000 years.

To accelerate the curing of concrete, accelerators often include calcium chloride, or aluminum sulfate or other acidic materials in an amount not to exceed 2% by weight. To make concrete cure slowly add a “set retarder”.  Most concrete retarders are relatively innocuous sucrose- (sugar-) based chemicals, added in proportions of .03% to .15%. Sugar addition increased the surface area and altered the pore size distribution of cement pastes. Sugar not only quickens the rate of cement paste hydration (after an initial set retardation), it alters the microstructure of calcium-silicate-hydrate. Some additional materials used to retard the set of a concrete mixture are lignin, borax, sugar, tartaric acid, and salt.
Factoid – If a volume of more then 20% of the retarding agent is used it works as an accelerator.
Alkali (sodium hydroxide NaOH and potassium hydroxide KOH) is a natural component of concrete. New, wet concrete has a high alkalinity with a pH reading of 12-14 but typically drops with the carbonation of the concrete. More cement means more hydrates that need leeching, and contrary to common sense, the higher the aggregate to cement ratio, the stronger concrete becomes. Sodium hydroxide(NaOH), also known as lye or caustic soda or sodium hydrate, is a caustic metallic base. Forming a strongly alkaline solution when dissolved in a solvent such as water. Sodium hydroxide is also the most common base used in chemical laboratories, and it is also widely used as a drain cleaner. This initial high pH is deadly if introduced to the display tank without a water bath cure. It also inhibits the settlement and growth of many species of marine life including some larval corals. . Each full digit increase (i.e. 7.0 to 8.0) is a tenfold increase in pH. A seemingly inconsequential increase of 9.0 to 9.2, is nearly twice as alkaline.

Concretes strength is inversely related to the ratio of water to cement. Low water-to-cement ratios produce higher strengths. Too much water in the mix will contribute to early flaking and spalling of the surface. When making Diy Rock we prefer a dryer concrete mix that allows for more crevices and nooks that are created while making the concrete. The hydration of the cement creates "pores" and "capillaries" in the cement matrix that once cured will wick water from the outside of the concrete in to center. The combination of these two effects are what give the Diy rock a balance between porosity for biological filtration and decorative support.
To aid with the ruduction of pH in cement and increase strength prozzolans are added to the concrete. Pozzolans are siliceous and aluminous materials, which in themselves possess little or no cementitious properties, but will chemically react with the calcium hydroxide in Portland Cement at ordinary temperatures to form compounds possessing cementitious properties. Pozzalanic materials can help to neutralize the surface pH by combining with the free lime and also providing for better bonding between aggregates, thus making the concrete stronger.  Such materials include coal combustion fly ash, diatomaceous earth, clays, shales, pumicites, micro-silica, among others. Some pozzolans control or reduce the alkali-aggregate reaction where reactive aggregates and high-alkali cement are used.
New technologies that have promise for the aquarist are the use of photocatalysts as additives in concrete. Photocatalysts are additives that allow concrete to keep clean. They decompose organic material on the concrete’s surface. What’s more, they reduce air pollution by scouring nitrous oxide from the air. (Not available commercially yet) Strong sunlight or ultraviolet light decomposes many organic materials in a slow, natural process. Photocatalysts speed up this process and, like other types of catalysts, stimulate a chemical transformation without being consumed or worn-out by the reaction. When used on or in a concrete structure, photocatalysts decompose organic materials that foul the surface. The organic compounds affected by photocatalysts include dirt (soot, grime, oil and particulates) biological organisms (mold, algae, bacteria and allergens), air-borne pollutants (VOCs including formaldehyde and benzene; tobacco smoke; and the nitrous oxides (NOx) and sulfuric oxides (SOx) that are significant factors in smog), and even the chemicals that cause odors. The catalyzed compounds break down into oxygen, carbon dioxide, water, sulfate, nitrate and other molecules that are either beneficial to or at have a relatively benign impact on the environment. Most inorganic pollutants and stains, including rust, are not catalyzed.
Factoid: The Romans made the first concrete in 500BC.

Types of Concrete:
Though all portland cement is basically the same, many types of cement are manufactured to meet different physical and chemical requirements for specific applications.

Type I General-purpose portland cement suitable for most uses.
Type II Moderate sulfate resistance. Life expectancy in the marine environment of 20 to 35 years
Type III Cement provides high strength at an early state, usually in a week or less.
Type IV Moderate heat during hydration that is used for massive concrete structures such as dams.
Type V Resists chemical attack by sulfates. Seawater contains 150 to 1500 ppm of sulfates.
Type GU - General Use
Type HE - High Early-Strength
Type MS - Moderate Sulfate Resistance
Type HS - High Sulfate Resistance
Type MH - Moderate Heat of Hydration
Type LH - Low Heat of Hydration 
Type HAC - High Alumina Content
Type S - Hydrated Lime, higher calcium content, (calcium hydroxide), Faster cure
Types IA, IIA and IIIA – Cements used to make air-entrained concrete. They have the same properties as types I, II, and III, except that they have small quantities of air-entrained materials combined with them.

White portland cement is made from raw materials containing little or no iron or manganese. (The substances that give gray cement its color.) Thorite often used in online articles is hydraulic cement that will have a faster cure time. Commonly branded as Quikcrete, it cost more the typical type II Portland, but the cure time is faster. Certified for use in wells and cisterns, it is safe for aquarium use. The water-stop cement isn't different from standard portland as far as porosity goes. The property that makes this product ideal for waterproofing is the quick setting time and the ability to place it on a wet area, and it will still cure. Polymer-modified mixtures (sealbond) are also stronger, bond better, with no shrinkage or cracking. None of these features alter the pore structure of the mix. The basic difference in these mixes is rapid setting mixtures can be used in a couple of days, with no PH swings, while standard portland mixes require a month dry curing and a month of wet curing (purging).

Appropriate Aggregate
All aggregates should be washed to remove any small particles and free silica. If there is a question as to the whether the aggregate contain phosphates or silica give the aggregate a acid bath and then soak in fresh water.

Sand - Sand makes cement stronger. You may also find that sand is a great casting medium and that you can get crazy shapes with damp sand. Any “clean” sand will work but avoid sands that are dark in color as they may contain metals
Aragonite – preferred sand but is the most expensive.
Limestone Sand/Pulverized Limestone – used in sand beds and DSB with success.
Play sand - most play sands will be made of quartz and so basically inert.
Play box sand – works well same as play sand.
Any white Sand – Avoid dark grain sands as the may contain heavy metals.
Sand Blasting sand - (casting sand) sugar fine, can be used for filtration, 99% pure Industrial Quartz.
Plastic shavings - PVC, Plexiglas and Lexan drill shavings.
Sodium Bicarbonate or Sodium Carbonate.
Perlite – Lightweight and inert.
Glass Sand - recycled product.
Calcium Carbonate, Aglime, Dolomite – Large grain size preferred, Comes in calcium based (preferred) and granite based.
Hydrated Lime – Reduces alumina content, boosts calcium, rocks more resistant to sulfate.
Vermiculite – Bulk insulation, also an aggregate in insulating and plaster and in insulating concrete.
Crushed Coral – Makes realistic rock and is coral so has a high over-all calcium content.
Oyster Shell – Common Koi canister filter media. It removes phosphate through both chemical composition, and structure.
Salt – Discovered by Travis Stevens (RC) – Solar Salt Crystals (Water Softener Salt). Side effects of salt use: salt acts as a set retarder and if excess amounts are used or overworked into the mix; the cement gets weakened.
Micro-silica - AKA Silica fume (used by Reef Balls) Use a Max of 10% silica fume by volume or 5% by weight. The concrete used to make Reef Balls features W.R. Grace's Force 10,000 micro silica to create a super high strength, abrasion resistant, concrete that has a pH similar to natural sea water.
Styrofoam – Lightweight and inert
Great Stuff Foam – Lightweight and inert

Reinforcement and Rebar
· Fishing line, Weed trimmer line
· Structural Support Rods / PVC / Acrylic (drill ½ inch holes throughout PVC)
· "Concrete fiber" (nylon hair strands), Fiberglass strands
· Gutter Guard
· Felt cloth strips
· Thin plastic hangers
· Plastic or acrylic rods – Available as bike flag holders or standard scrap acrylic.
· Nylon or plastic window screen

Great Casting materials
· Rubber fish lure worms
· Salt
· Sand
· Oyster shell
· Crushed coral, Old corals can be crushed up to give texture to the new rock.
· Balloons – Water filled or air filled. Leave some of the balloon exposed for easy removal.
· Latex gloves filled with air or water.
· Silicone / Plastic – Rubber bait worms. 

Do Not Use
Wood Dowels – Splits when trying to remove from cast concrete. Pain
Pasta – Wet Pasta is nasty and Dry pasta should only be used on the outside as it becomes hard to remove and may crack the concrete as it hydrates.

Tip: If you dampen the casting material most will not stick to the rock. This helps went you want to add layers to the rock. Additional concrete will adhere very well to fresh concrete but not to the dry casting material.

Rock Recipes
Ingredients are measured by volume.
Typical construction mix 1:2:4 (cement: sand: rock aggregate)
Strong mix - 1:2:2:2 (cement: sand: crushed coral or oyster shell, aggregate)
Porous mix – 1:2:2:1 (cement: sand: crushed coral or oyster shell: salt)
Lightweight and Porous mix – 1:2:1:1:2 (cement: sand: crushed coral or oyster shell: salt: Styrofoam)
Insane Reefer’s (RC) preferred recipe - 1.5:1.5:1:1 (cement: sand: crushed coral/shell mix: salt)
a1maps preferred recipe – 1:1:1:1: .5: 5%: 1% (cement: sand: coral/shell mix: salt: Styrofoam: 5% sugar: 1% Diatomaceous earth.)

I prefer to use a quick cure cement at the curing of the rock is faster. Since the sugar and the salt act as a set retarder I get extra time till the cement sets up. Sugar addition also increased the surface area and alters the pore size distribution of cement pastes. Sugar not only quickens the rate of cement paste hydration (after an initial set retardation), it alters the microstructure of calcium-silicate-hydrate. Any left over sugar will act as fuel for bacteria growth when added to the tank. 5% sugar is measured by volume so if you use and 8oz drinking cup to measure with you will need to use roughly .4 oz of sugar per 8oz of cement. The salt is mixed in last right before casting, as it is corrosive to concrete. For outer layers I add additional salt to the cement to make more porous The diatomaceous earth is a prozzolan, which lowers the pH and should make the concrete stronger and ready faster.

Tools needed
· Latex gloves – cement is caustic
· Dust mask
· Trowel
· Small cup for measuring cement/sand/salt/etc…
· Water – Do not use a hose. Cement goes from “too dry” to “too wet” very fast.
· Minimum of two 5-gal buckets or plastic lined cardboard boxes. The Styrofoam boxes fish come in make great casting boxes.
· Mixing tub
· Tarp and plastic trash bags
· Cement and appropriate aggregates (salt, sand, crushed coral, oyster shell, rocks)
· Casting sand or casting material
· PVC pipe, 45 and 90 elbows, Ts – The small the diameter the better.
· ¼ and ½ inch drill bit – to drill holes in PVC and to make frag holes.
· Stainless steel or aluminum wire – To poke holes into the rock while wet.

Mixing and then Shaping Diy Rock
Step 1: Prepare the area.
Put the tarp down to protect the work area from spills. Have running water available and clean tools off immediately. Use a dust mask while working with dry power cement to protect your lungs. Use latex or chemical resistant gloves while working with cement. Set up your mixing bucket and your casting buckets (or trash bags). You will need multiple buckets to cast the rock in. Once the rock is cast in the casting material it must sit till it has become hard. Fill these containers with 2-3 inches of casting material and leave remaining casting material aside to build up as you put cement into the casting bucket.

Step 2: Measure out your dry ingredients and water. Mix your dry ingredients together (excluding salt) in your mixing bucket until they are evenly mixed. Add water slowly. Pour water in slowly and mix. Concrete goes from too dry to way too wet very quickly. You want a slump with the consistency of clumpy dry oatmeal. The cement should not flow, if it does add more cement or sand.

Step 3: Optional – Fold in the rock salt. Notice the word “fold” vs. “mix”; you must work fast so that little salt dissolves from the water, but be able to work long enough to be able to get the rock salt evenly dispersed into the cement. The end product should be able to hold its shape relatively easily. Adding the salt will make the concrete seem a little looser or wetter. This is because the salt is dissolving and is acting as a set retarder. The more you mess with the rocks, the weaker they will set.

Step 4: Once mixed begin to layer the concrete. In the casting bucket dig irregular and creative shaped molds in the slightly dampened sand. depression in the material. Using rubber gloves, place lumps of concrete into the casting material you prepared earlier. Layer each clump of concrete onto bare concrete from a previous layer. There is no sculpting needed. Randomness, layered rock or even multiple smaller pieces cemented together look the best. Dribble cement in layers while placing casting material or other shaping tools in between layers of concrete. This will make the rock more porous and will create interconnecting caves and tunnels. Dribble your next layer of cement mix over that and keep making holes and tunnels with the intermittently placed pockets of damp sand or salt. Add more casting material around the sides as you build your rock. The casting material will add dimension and keep the shape till the concrete hardens. You can make neat “cliff-face” striations if you take a handful of salt, and lay it just along the top edge of wet cement, forming a narrow line of salt along the edge, laying a thin layer of cement over the salt, and repeating this to form, on the outer edge of your rock, a sort of cliff that looks to be cut by water action. Making a semi-flat Diy rock that will bridge the gap between 2 larger Diy rocks can make a large cliff. As you cast your rock, use wire to poke lots of little tunnels all through the rock; this will make the rocks extra porous, and give micro fauna lots of places to hide and propagate in-tank, as well as allowing more water to move through the rock.
You can overlap concrete and casting material to create ledges, shelves, caves, arches and branching coral extensions (see below). A certain portion of the molding material will remain on the rocks - this can usually be removed by a good scrubbing with a plastic or fine wire, bristle brush. I prefer to leave the casting material because I like the color and texture.
Tips:
· If you use Quikcrete or another fast setting cement make small batches and work in layers. Cement will start to harden in as little as 3 minutes.
· For base rock put divots in casting material to reduce dead spots under rock.
· Dampen casting material to hydrated concrete and allow for easy removal.
· Add trails of sand through the inside of the concrete and after dry wash out. This will create hollow lacy thin cave rock.
· When concrete is able to be handled use drill to put ¼ inch holes into the rock to hold frag plugs.
· DO NOT Wet Salt, if it is used as a mold material - this means when working with salt, do not add water to the casting box as you would with clay or sand.
· Thinner than an inch is likely to break, unless you use rebar such as gutter guard or PVC.
· If you want to interconnect multiple rocks without epoxy use PVC as a coupler between rocks. Use a small diameter PVC and stick it into the wet concrete leaving about 1½ exposed. When the rock is cured, you can “lock together” pieces by wrapping the exposed PVC with plastic and then cast the second rock, making sure to get a good fit around the PVC joint. (easily removable)
· Drill existing rocks and put pegs on then to attach to Diy rock.
· Flatter surfaces and shallow bowls in larger rock shapes can make Frag placement easier.
· Cemented Nylon String - Makes realistic tube worm/duster tubes. Make a thin paste of just cement, and dip small lengths of the sting in. Wipe excess off between fingers and lay onto the rock in desired figure.

Arches
Arches are easy to create and can add a neat effect to your aquascaping. Arches are easier to make on there sides so you can see how large the arch is going to be. Start by filling a box with 4 inches of your casting material. Make a depression in the sand the size you want the arch to be. Dribble in the depression with concrete using the same technique used to make regular rocks. Build up the sides with casting material as you add concrete. For the concrete mix use more aggregate (shell or gravel) and less portland in the mix, for greater strength, better curing, and fewer cracks in the arch.
Another way to make an arch is to make it up out of 3 pieces that are joined with a plastic rod and then cemented together. You could also use rocks and PVC pipe to make the structure, and fill in the gaps with concrete mix.

Towers
Towers are stacked rocks. There are 2 ways to make them.
Take existing rocks that have been made and drill a hole in the center to allow for a support rod to be inserted. (PVC or acrylic) Then cement the rocks together.
If you want to make a tower from the start you can save yourself the hassle of drilling through the rock and create a layered tower from the start. Take an appropriate length PVC pipe and drill many holes into it. Make a small concrete base and insert the PVC into. Let set. Add more casting material as your tower rises up. As each layer sets add another.
Tips
· Use quickset cement.
· Use different casting materials as you move up your tower will add nice dimension and since most corals are built up over centuries they have different textures at different levels. 
· Towers don’t have to go large to small. Have sections that jut out to make cliffs and overhangs. 

Walls and Backdrops
Most walls are created to hide plumbing, overflows or sides of a tank. Also smaller footprint tanks make it hard to stack large quantities of rock while maintaining an open flow. By making a rock wall you can use space that would normally go unused and leave more take open for fish to swim.  It is not feasible to make a wall as one piece. Concrete is very heavy and most tanks have a cross brace. It is better to make a wall out of smaller interlocking pieces.
Create a template for the wall you wish to make out of wood or acrylic. Leave holes for any plumbing that comes through the tank wall. Cover the template in plastic to facilitate easy removal. Start from one corner and make a rock as you normally would except leave the edge tapered or angled. You can leave the edge as zigzagged as you want the taper will lock the wall pieces together. There are no straight lines in nature and you eye will be drawn to the seam if you leave it straight. Use sand to hold the rock while setting. Use wax paper or plastic wrap to separate on piece from another. Create the adjoining rock piece in place only separated by plastic. This will ensure a tight fit. As you progress you will need to alter which side you will leave the tapered edge on. This will ensure a seamless fit. Gutter guard or PVC can be embedded into the concrete to give extra support. A variety of surface textures that enhance the settlement of marine life are available. A popular surface texture is made by spraying sugar water onto the surfaces of the mold before casting. After the cement mixture hardens, the mold panels are removed and the last ½ inch of concrete remains unhardened. Rinsing the wall with a garden hose exposes a rough stony surface. Wall covering sheets can be glued with silicone to the back wall of your tank.
Tips:
· Don’t use salt in wall concrete mix
· Use a quickset, as it will speed up the creation of the wall.
· Once you have your pieces made, please wait at least a week before removing your new pieces from their cast.   This will help ensure the pieces are hardened enough to be handled.
· Add multiple coats to add shelves, ledges and other dimension to the rock wall

Branching Pieces
Branching rock and coral skeletons are the hardest Diy rock types to make. These take a lot of practice and a lot of scrap concrete to be recycled into future rocks.
Dip Method
I find this method the easiest to start with as there is less skill needed. Start with PVC, plastic coat hanger or another thin malleable material. Drill holes in the Plastic to allow the concrete to adhere easier. Use zip ties to attack pieces of plastic together. Straight lengths of PVC or Plastic can be bent using a torch. You can bend PVC into believable shapes using heat from either a propane torch and a couple of pairs of pliers.  Use caution molten plastic is very hot. Remember there are no straight lines in nature. Tie fishing line around the base of the structure. (To hang) Roughen up the PVC or plastic with sand paper to allow better adhesion by the cement. Make your concrete mix wetter then for Diy rocks and it should contain only small aggregates. The wetter cement is needed to dip the coral structure into. The wet concrete will stick to most of the structure. Don’t worry if there are sections that are not covered, these will get covered in additional dips. After each dip hang the structure up to set.
Tips:
· Plastic drinking straws and mixing straws are excellent for smaller detail pieces.
· Use a quickset cement to speed up dips.

Pinch Method
To make branching base pieces, dig out the shapes for your rockwork in your casting material. You will either be making your rock upside down or right side up. This depends on what you’re trying to make. If you’re making a rock that has fairly intricate projections or branches, make it upside down. Upside down is that the top of your rock will be the first part of the rock that you are creating.  Place small pieces of the concrete into the depressions you dug out.  After you get the shape you want, make sure to bury the sides with any extra sand. The upper more decorative pieces don't utilize this method because you have to "pinch" the cement together to ensure that plenty of cement is always in contact with itself and the rest of the new structure that you're making. Let the base piece set. Once hardened clean any casting material off the ends where you will be adding branches. New cement sets best to fresh cement. While lying on its side start to elongate the branch; use sand to give shape and texture. Let set. Continue adding branches making sure to always have enough cement in contact with itself. To do this, carefully add more cement and shape it with your fingers. Make sure that each branch is contacting an adequate amount of wet cement of another branch. If you don't it will break off later, especially if you make it real thin. It takes a little practice to accomplish this and get a feel for how thick each section needs to be in order to keep it strong. Turn coral piece over and repeat until complete
Tips:
· Stronger Branch rocks can be made with plastic hangers in the center. Heat them and bend into the shape you want then use them for reinforcement in the center of the branches.

Step 5: Once you have completed you rock Cover the entire rock in damp casting material. (If you cast in salt eliminate this step) Cover the buckets with a lid or close up the plastic trash bag. The rocks will need to dry cure for a while depending on the type of cement used. The rocks should be re-hydrated every second day. The rocks are fine outside in the summer as the heat and humidity will aid in the curing. 

Salt Release and The Very Important 2-Part Cure
Curing is one of the most important steps in reef rock making, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete’s temperature stays within a suitable range. During the curing period-from five to seven days the concrete surface needs to be kept moist to permit the hydration process. Leave the rock in a warm, damp place for 7-28 days. The longer you leave it alone the more able it will be to withstand chemical attacks and the stronger it will be. Wrap new concrete in plastic garbage bags keep in closed buckets to hold in moisture. Add moisture to the bags/buckets periodically as repeated wet-dry cycles promote carbonation. Once on the surface, calcium hydroxide chemically reacts with carbon dioxide and is converted into calcium carbonate. (Good) This dry time is important.

If you used salt in your rock, it must be removed. Salt will release in hot water much easier than it will in cold water. After the rock has cured for a minimum of 14 days (longer for Type I and II) put the rock in a bucket of water with a power head and an extra aquarium heater to bring the temp up. Depending on the thickness of the piece it may take up to 2 weeks for the salt to release. Do not use Ro water, as it is ion depleted and will weaken the rock. Place rock in cool water and allow heater to heat up the water slowly. Never put fresh concrete into hot water as it will weaken and create hairline cracks. Leaving the water outside during the summer works well as the temperature will be around 80. Replace the water 3 times per day for the first 2 days, then once per day for a week. Even though this is to remove salt it will also be the start of the purging process to reduce the pH of the rock to 8.5. After a week the water changes can be done every 3rd day. Keep doing this till you no longer see white scum on the water surface. White scum is calcium carbonate. As the calcium oxide and calcium hydroxide combine with CO2 at the water's surface it creates calcium carconate. This crust gets thinner with each subsequent water change.

After you have changed the water many times the white surface scum will stop. Empty the bucket and clean the scum off the inside. Add fresh water and let sit for 2 days and then test the pH. When the pH stays consistent around < 8.5, replace the water with used saltwater. This encourages you to do a water change on your main tank and gives you a use for the water. Test the pH of the water immediately and again in 2 days. If after 2 days the water stays at a stable pH of < 8.5 it is safe to use. If the pH remains high then continue curing.

Is It Done Yet?
The amount of time it will take to complete the 2nd part of curing varies greatly depending on thickness and how well you mixed the cement. Once the rock is at an acceptable pH, wash the finished product with a weak acid to etch the concrete. (Muriatic acid or vinegar). This will stabilize and seal the rock. Before adding the rock to the tank, give the rock one final wash to remove any loose material and to neutralize the acid. Scrub the outside of your rocks with a stiff bristle brush; this will loosen the weakest stuff and get rid of it without shedding it all over your tank.  Caution Use proper care when working with acid. The acid and vapors can cause serious burns. Vinegar is safer to use but may need to soak longer. Save the small pieces that fall off; they make great frag plugs.

Steam Curing at Atmosphere
Mini Rock Sauna - First Tested January 9th, 2008 By Insane Reefer at Reef Central http://reefcentral.com/forums/

“The purpose of the Mini Rock Sauna (MRS) is to allow the hobbyist to create MLR (Manufactured (DIY) Live Rock) in a very short time-frame by using what I’ve dubbed as the Jiffy Rock Method (JRM). Previous efforts with the JRM produced traditional type rock, using traditional materials, that could be used in the aquarium in as little as 9 days…. By following the cement block industries methods for steam curing cement blocks that are equivalent to mature block of 28 days of age, the new and improved JRM has less potential for possible future rock failure.” Insane Reefer.

Faux Coralline Algae and Effects
The main problem people seem to dislike about Diy rock is the length of time it takes for the rock to become live and covered in coraline. To make the rock more interesting while we wait for real coralline and corals to dominate, the rock can be colored. I prefer to wait for the rock to be naturally covered and even the choice of aggregates can affect the final rock. Many have used cement colorants, grout colorants, hobby paint, and even kool-aide. Apply the colorant in blotches similar to the look that coraline algae has when it populates your natural live rock. The color purple matches that of live rock seems to math the color of coraline best. Most colors will fade so the rock should be darkened several shaded deeper to achieve the desired results. Colorants and dyes are available from building supply stores or concrete manufactures. If you're really ambitious, you can paint the surface to look like coraline algae with epoxy or two-step polyurethane paint. I don't bother as coraline grows in about six months.
Use lag bolts to make faux fossils and machine screws to make wormholes and coral plug bases. You can have pressure fit plug and play coral anchors with 1/8" acrylic rods, or you can imbed plastic nuts in the cement and affix a corresponding bolt to the coral. You could also bond plastic nuts within the concrete, and affix a corresponding plastic screw to corals.

It’s “Alive”
The Diy Rock is sterile when first introduced into the tank. Everything that ultimately ends up in and on the rock comes from seeding the rock. Don’t expect coraline in the first week. It will follow a similar path as your new tank. The most opportunistic life forms will propagate the rock first. Diatoms will surely be the first thing on the rock; Followed by bacteria, film algae, green algaes, some nuisance hair algae, micro-fauna, cyanobacteria, sponges/tunicates, and feather dusters. The best way to seed the new rock is through your local reef club. It will take about 6 months to have good growth on the Diy rock. After a year you can’t tell the difference between the Diy Rock and real live rock.

Combination Live Rock and Cement

There are a lot of places to get info on Diy Rock. 2 reefers from Reef Central, Insane Reefer and Mr Wilson in particular have experimented and tested different concrete mixes and have offered their knowledge to all. I have learned a lot by experimenting with concrete but they have helped me with more information then I could have found on my own.

Links on Rock Making
http://www.garf.org
http://www.garf.org/news17p1.html
http://www.geocities.com/CapeCanaveral/
http://reefcentral.com/forums/
http://www.reefcentral.com/forums/
http://www.3reef.com/forums/i-made/
http://www.reefcentral.com/forums/
http://stores.ebay.com/
http://www.earthpigments.com/
http://stores.ebay.com/
Links on Phosphate Leaching
http://reefkeeping.com/issues/2006-09/rhf/index.php#10
http://reefcentral.com/forums/showt...threadid=489121
Acids and Bases
http://www.visionlearning.com/library/module_viewer.php?mid=58