emilecilliers
New member
Here is something I picked up on the net.Give your thoughts and have anyone tried this?
Greetings fellow rockers and future rockers! It's time to share some tips on making and curing reef-safe cement rocks and for growing some great cement live rock of your own. Some of you have been to scared to try cement rocks (like I was), since cement can have some dangerous qualities. We'll cover the problems and simple solutions so that you can charge ahead in full confidence when making and using your own live cement rocks.
Why use cement rocks for your aquarium?
Natural live rock is very expensive but cement rocks are quite easy to make and can be made very cheaply if you know what to use. Some people have just used cheap cement "post mix" to make rocks for freshwater aquariums and even for saltwater aquarium use. Post mix is a dry bagged mix of Portland cement powder, sand and gravel that you just add water to, stir and form it into rocks. However, you may be much safer not using ordinary gravel that is contained in post mixes which may have heavy metals that could dissolve more readily in saltwater. I prefer to use sand and gravel like crushed coral, aragonite sand, or crushed oyster shell. All three work very well. You can mix these with any cement powder I use Portland cement which is the easiest to find at places like B&Q or other builder's supply shops. It is sometimes very hard to find just the right size and shapes of wild live rocks to make the perfect aquascape in your aquarium but some very nice shapes and sizes can be made from cement.
A simple, cheap recipe for making cement rocks
Try this good, simple, basic recipe for making the cheapest porous cement reef rocks around.
You will need...
• A bucket
• 1 Pair of rubber gloves
• Wooden spoon or hand held gardening shovel
• A plastic tray or tub half filled with sand or crushed oyster shell (use this as a mould)
• Portland cement
• Crushed oyster shell
Using a large bucket, add 5 cups of common easy to find Portland cement from B&Q or any building supply shop. Add 20 cups of crushed oyster shell. Add 5.5 cups of water and mix very thoroughly with a shovel or wooden spoon. Use rubber gloves to protect your hands from chemical burning due to extended exposure to the high pH of the fresh cement - this is like soaking your hands in supersaturated kalkwasser! Tip the bucket on a 45 degree angle and rotate or roll it to help tumble and mix the cement well. If the mix is too dry add a little more water (slowly). I try for a final mix with the consistency of cottage cheese. Others go a bit wetter than this, but not too slushy. You can get crushed oyster shell at a farm feed shop. It is used as a very common chicken feed supplement. And that, my friend, is why THIS cement reef rock recipe is so "cheep, cheep, cheep"!
Do not make the final product too runny or you will not be able to shape it into nice looking irregular shapes. An almost slushy mixture that will still stand up just a little and take some shape (just a bit) is just right for molding in a damp sand bed. In fact, a wetter mix not only assures that the silicates in the cement mix get hydrated and bound, but a slightly wetter mix will produce more micro-pores or capillaries throughout the cement for better bacterial colonization inside the rocks. On the other hand, this can also weaken the cement just a bit, but usually not critically so. Still, don't make it too dry or the cement will have too many large airspace gaps between sand or crushed oyster shell bits and it will then be just as weak or weaker than the mix that is too wet. Maximum hardness (for practical purposes) is mostly reached after about a month of curing. Now, using rubber gloves, scoop handfuls of it into a bed of dampened sand (or substitute, like damp crushed oyster shell!) for molding and shaping your cement into reef rocks.
Curing cement rocks
Curing your new cement rocks is your next, and biggest concern, if you do not properly or adequately cure your cement rocks before using, you could end up killing everything in your aquarium. New cement rocks will leach heavy amounts of calcium oxide and calcium hydroxide (the two forms of kalkwasser - K.W. for short). You wouldn't dump a whole bunch of K.W. in your tank would you? So, you need to soak the cement as it cures since more K.W. is released from cement as it hydrates/cures, and it does take time. Patience is important here.
Quick cures using vinegar or acid will just cost you extra money and do not really "cure" the cement. People have killed their marine life by using these quick cures when using a lot of cement rock at once. Sure, you can get away with using quite small volumes of cement rock with these quick cures, if the amount of K.W. being leached after the "cure" is not too high for the volume of your aquarium. The quick acid cures lower the pH some, but tend to take just as long or longer to really finish curing after this! The most dramatic part of real curing takes place in the first week, but significant hydrating (curing) still takes place for at least the first month or longer. You can witness this by putting your cement rocks in fresh tap water (after they are about two to seven days old) and doing weekly water changes while testing the pH. Depending on the cement to water ratio that you cure them in, they will leach enough K.W. into the water in the first week to raise the pH up to maybe 10, 11 or higher! They also leach silicates when they are curing. This doesn't sound like what you want in your reef aquarium? Don't let this make you nervous, because once the cement rocks have had ample time to cure, they are leaching virtually no silicates or K.W. and are VERY reef-safe! You just have to be patient and test the pH of the curing water each week until it comes down below 8 and stays there.
Bubbling CO2 through the curing water will lower the pH since the CO2 combines with the K.W. to make calcium carbonate in the water and inside the rocks. This strengthens the rocks. It is really not necessary to use CO2 though a few people have. You can just use a fine airstone to bubble regular air through the water to achieve the same result. Curing in stagnant water is slightly slower, but has one advantage. You will know when the cement rocks are still leaching K.W. since you will not be forcing the removal of K.W. with CO2 and masking the pH. Even if you use an air bubbler while curing, be sure to turn it off for a couple of days when you think the cement is cured so you can tell if K.W. is building up in the water. A rising pH in stagnant curing water will tell you if your cement is still curing significantly. Curing in plain water is really the easiest and cheapest method but it does take a bit more time.
Basically speaking it is best or safest to Give your cement rocks about six weeks of curing time in tap water and then two weeks in saltwater (you could use your waste water from your usual water change), before adding them to your aquarium. I just lost some of you when I said "... then two weeks in saltwater...", right? After you are done curing, and it may be quicker or longer than six weeks (You have to test YOUR curing water pH to see for sure.), you will notice that when you put one of your cured cement rocks in a jug or bucket of stagnant saltwater from your aquarium that the pH raises to about 8.6 or higher by the next day! We call this pH rebound. It can take a couple of extra weeks in saltwater for this pH rebound to subside. I do not know why the rocks start leaching more K.W. when you put them in saltwater after a freshwater cure. Any suggestions from chemists out there? I'm obviously not one myself.
More cement curing ideas
I have heard of using an airstone in fresh water and bubbling the curing water with the cement rocks in it for one week and then change the water and add baking soda and continue bubbling and adding baking soda until the pH comes down, I don't know how long it takes but it could be worth a go. you could stop when the pH comes down below 8.3 which WILL support fish and corals just fine, as long as your tank has good aeration to equal what the airstone you were curing with does. Silicate leaching is also pretty much done by then (so I've heard). My concern is still that with K.W. leaching and boosting the pH to around 8.2, you could end up binding your aragonite sand when the calcium precipitates form the water and forms calcite in the sand grains. Excess K.W. dosing can do this even more easily than buffers, or at least at a lower KH/alkalinity. I still feel much better about taking the pH lower than 8 in stagnant water conditions before adding the cement rocks to an aquarium with aragonite sand. Besides, once you change the fresh water with salt water for a final two week curing, the cement rocks that were previously raising the ph of fresh water to a level of less than 8 pH in four days in stagnant saltwater will now raise the pH of the new saltwater change to over 8.6 or 8.7 in one or two days sitting in stagnant tank water (saltwater). After this final two weeks curing in salt water with an airstone running to form calcium carbonate and lower the pH, you will not get a dramatic rise in pH anymore when you turn off the airpump, which indicates that curing and leaching of K.W. and silicates are practically done and the rock is safe to use in a well aerated aquarium..
One more note on curing time. A few factors will affect the curing time of your cement rocks. For starters, small or flat rocks cure quicker. The pH of your tap water can speed or slow curing. My tapwater is about 7.6 to 8.0 pH and is high in calcium, magnesium and other elements that make water "hard". I get quicker curing times in this tapwater than people using soft water or R.O. water. Soft water with a low pH and with very low amounts of these dissolved solids will actually take longer to cure. Some people have even reported six months of curing in very soft or R.O. water! I suspect that you might not get the pH rebound with saltwater after a complete curing in R.O. water, but have not been able to verify this (yet).
Different materials take longer to cure also. Silica sand cement seems to cure faster, while aragonite cement cures a bit slower and crushed oyster shell cement even a bit slower than that. I still like the oyster shell cement best. It is cheap and has great porous texture.
No matter what method you use to cure your cement rocks, be sure to test the rocks in stagnant water for a few days to verify that the pH is not rising dangerously. WE are working on another accelerated (and SAFE) method for curing cement rocks and will pass it on to others and you if it works out.
When the rock has cured the PH should be 8.3 or under, correct?
Yes, but you can get away with slightly higher, but I prefer below 8, and even 7.5 to 7.7 holding steady in stagnat water for four days or longer (in salt water) for really cured cement rock. But, you can get away with just the freshwater cure and make sure you have good aeration to keep the pH down. You will see the KH in your tank or curing container of saltwater climb if the rock is still leaching. People do vary it a little, but the aragonite sand can get crystalized a bit with calcite even if it does not clump, so if you like the benefits of aragonite sand buffering and adding calcium, then be cautious on this point of jumping the gun.
Why are oyster shells a great substrate if they are high in phosphate?
They are high in phosphate and have silicates too, but others and I have not had a leaching problem once they are cured in cement.
How does the porosity of cement rock compare with natural rock? Have any measurements been made?
Some of my oyster shell rock is more porous than most wild rock. But, you can vary this as you like. The oyster shell is what makes it so easy to get the minor air pockets all over that allow tap water to run right through.
Any recomendations for better colors besides the dull grey concrete?
Yeh, but it costs... You can use white Riverside cement rather than the regular (and much cheaper) grey Portland cement. But I find that white live rock undersides eventually turn about the same color as the Portland cement anyway.
When will Coraline algae start to grow on new liverocks? Also what does Coraline algae looks like (shape, size, color) when it first appears on the rock?
Coraline algae starts growing immediately if spores are floating around in your water. You will see them after about 7 to 10 days of the new rock being in your tank if conditions are good - little pink, purple spots.
Do some polyps or corals attach faster to the rock?
It has worked well for me with any coral polyps I have tried with other rocks. I have made small cookies or blobs in the sand molding bed and then I can use these to attach corals to.
Concrete has capillary porosity. Since only the outside of the rocks isn't covered in concrete, how can these rocks sustain comparable amounts of bacteria?
I suppose if you make your rocks too solid or with not enough water or pourous holes from using oyster shell ... that you could have less bacteria .G.A.R.F. has had good luck with one of their tanks with 90% cement rock, but hey do not have a 100% one yet, but I don't think that matters.Jake Levi is the only person I know of with tanks with 100% cement rock and he says they do well. Others might have them too?
If you are adding cured rock do you discourage adding K.W. as a safety precaution?
Yes, I would discourage adding extra K.W. since you could get a minor leaching from the rock for a little while and if you only cure your cement rocks in fresh water and don't do a "saltwater follow-up" then you will get a K.W. spike when you put the cured cement rocks in to your saltwater aquarium.
Do you get the same amount of coraline growth on the homemade rock compared to natural rock?
Yes, I do, if I don't include coraline eating hermits with them. If your numbers of coraline eating hermits in your tank are low, then it just takes a lot longer for the coraline to get a foothold and grow - probably the hardier slow growing varieties that are not as tasty?
But if your numbers of these hermits are high, then you will really have a long wait to see much coraline growth.
My biggest question is, simply, why?
First, you can gain nice porousity with cement using the technique listed here. Any life in the live rock that will not reproduce and spread to your new cement rock will eventually die and be gone anyway, so if this was really a problem then you would have to change your wild live rock all the time! YOU DO however need to use a small amount natural live rock to provide seed material for these new "dead" rocks or they will remain that way! It is very easy to do this almost without trying.
Greetings fellow rockers and future rockers! It's time to share some tips on making and curing reef-safe cement rocks and for growing some great cement live rock of your own. Some of you have been to scared to try cement rocks (like I was), since cement can have some dangerous qualities. We'll cover the problems and simple solutions so that you can charge ahead in full confidence when making and using your own live cement rocks.
Why use cement rocks for your aquarium?
Natural live rock is very expensive but cement rocks are quite easy to make and can be made very cheaply if you know what to use. Some people have just used cheap cement "post mix" to make rocks for freshwater aquariums and even for saltwater aquarium use. Post mix is a dry bagged mix of Portland cement powder, sand and gravel that you just add water to, stir and form it into rocks. However, you may be much safer not using ordinary gravel that is contained in post mixes which may have heavy metals that could dissolve more readily in saltwater. I prefer to use sand and gravel like crushed coral, aragonite sand, or crushed oyster shell. All three work very well. You can mix these with any cement powder I use Portland cement which is the easiest to find at places like B&Q or other builder's supply shops. It is sometimes very hard to find just the right size and shapes of wild live rocks to make the perfect aquascape in your aquarium but some very nice shapes and sizes can be made from cement.
A simple, cheap recipe for making cement rocks
Try this good, simple, basic recipe for making the cheapest porous cement reef rocks around.
You will need...
• A bucket
• 1 Pair of rubber gloves
• Wooden spoon or hand held gardening shovel
• A plastic tray or tub half filled with sand or crushed oyster shell (use this as a mould)
• Portland cement
• Crushed oyster shell
Using a large bucket, add 5 cups of common easy to find Portland cement from B&Q or any building supply shop. Add 20 cups of crushed oyster shell. Add 5.5 cups of water and mix very thoroughly with a shovel or wooden spoon. Use rubber gloves to protect your hands from chemical burning due to extended exposure to the high pH of the fresh cement - this is like soaking your hands in supersaturated kalkwasser! Tip the bucket on a 45 degree angle and rotate or roll it to help tumble and mix the cement well. If the mix is too dry add a little more water (slowly). I try for a final mix with the consistency of cottage cheese. Others go a bit wetter than this, but not too slushy. You can get crushed oyster shell at a farm feed shop. It is used as a very common chicken feed supplement. And that, my friend, is why THIS cement reef rock recipe is so "cheep, cheep, cheep"!
Do not make the final product too runny or you will not be able to shape it into nice looking irregular shapes. An almost slushy mixture that will still stand up just a little and take some shape (just a bit) is just right for molding in a damp sand bed. In fact, a wetter mix not only assures that the silicates in the cement mix get hydrated and bound, but a slightly wetter mix will produce more micro-pores or capillaries throughout the cement for better bacterial colonization inside the rocks. On the other hand, this can also weaken the cement just a bit, but usually not critically so. Still, don't make it too dry or the cement will have too many large airspace gaps between sand or crushed oyster shell bits and it will then be just as weak or weaker than the mix that is too wet. Maximum hardness (for practical purposes) is mostly reached after about a month of curing. Now, using rubber gloves, scoop handfuls of it into a bed of dampened sand (or substitute, like damp crushed oyster shell!) for molding and shaping your cement into reef rocks.
Curing cement rocks
Curing your new cement rocks is your next, and biggest concern, if you do not properly or adequately cure your cement rocks before using, you could end up killing everything in your aquarium. New cement rocks will leach heavy amounts of calcium oxide and calcium hydroxide (the two forms of kalkwasser - K.W. for short). You wouldn't dump a whole bunch of K.W. in your tank would you? So, you need to soak the cement as it cures since more K.W. is released from cement as it hydrates/cures, and it does take time. Patience is important here.
Quick cures using vinegar or acid will just cost you extra money and do not really "cure" the cement. People have killed their marine life by using these quick cures when using a lot of cement rock at once. Sure, you can get away with using quite small volumes of cement rock with these quick cures, if the amount of K.W. being leached after the "cure" is not too high for the volume of your aquarium. The quick acid cures lower the pH some, but tend to take just as long or longer to really finish curing after this! The most dramatic part of real curing takes place in the first week, but significant hydrating (curing) still takes place for at least the first month or longer. You can witness this by putting your cement rocks in fresh tap water (after they are about two to seven days old) and doing weekly water changes while testing the pH. Depending on the cement to water ratio that you cure them in, they will leach enough K.W. into the water in the first week to raise the pH up to maybe 10, 11 or higher! They also leach silicates when they are curing. This doesn't sound like what you want in your reef aquarium? Don't let this make you nervous, because once the cement rocks have had ample time to cure, they are leaching virtually no silicates or K.W. and are VERY reef-safe! You just have to be patient and test the pH of the curing water each week until it comes down below 8 and stays there.
Bubbling CO2 through the curing water will lower the pH since the CO2 combines with the K.W. to make calcium carbonate in the water and inside the rocks. This strengthens the rocks. It is really not necessary to use CO2 though a few people have. You can just use a fine airstone to bubble regular air through the water to achieve the same result. Curing in stagnant water is slightly slower, but has one advantage. You will know when the cement rocks are still leaching K.W. since you will not be forcing the removal of K.W. with CO2 and masking the pH. Even if you use an air bubbler while curing, be sure to turn it off for a couple of days when you think the cement is cured so you can tell if K.W. is building up in the water. A rising pH in stagnant curing water will tell you if your cement is still curing significantly. Curing in plain water is really the easiest and cheapest method but it does take a bit more time.
Basically speaking it is best or safest to Give your cement rocks about six weeks of curing time in tap water and then two weeks in saltwater (you could use your waste water from your usual water change), before adding them to your aquarium. I just lost some of you when I said "... then two weeks in saltwater...", right? After you are done curing, and it may be quicker or longer than six weeks (You have to test YOUR curing water pH to see for sure.), you will notice that when you put one of your cured cement rocks in a jug or bucket of stagnant saltwater from your aquarium that the pH raises to about 8.6 or higher by the next day! We call this pH rebound. It can take a couple of extra weeks in saltwater for this pH rebound to subside. I do not know why the rocks start leaching more K.W. when you put them in saltwater after a freshwater cure. Any suggestions from chemists out there? I'm obviously not one myself.
More cement curing ideas
I have heard of using an airstone in fresh water and bubbling the curing water with the cement rocks in it for one week and then change the water and add baking soda and continue bubbling and adding baking soda until the pH comes down, I don't know how long it takes but it could be worth a go. you could stop when the pH comes down below 8.3 which WILL support fish and corals just fine, as long as your tank has good aeration to equal what the airstone you were curing with does. Silicate leaching is also pretty much done by then (so I've heard). My concern is still that with K.W. leaching and boosting the pH to around 8.2, you could end up binding your aragonite sand when the calcium precipitates form the water and forms calcite in the sand grains. Excess K.W. dosing can do this even more easily than buffers, or at least at a lower KH/alkalinity. I still feel much better about taking the pH lower than 8 in stagnant water conditions before adding the cement rocks to an aquarium with aragonite sand. Besides, once you change the fresh water with salt water for a final two week curing, the cement rocks that were previously raising the ph of fresh water to a level of less than 8 pH in four days in stagnant saltwater will now raise the pH of the new saltwater change to over 8.6 or 8.7 in one or two days sitting in stagnant tank water (saltwater). After this final two weeks curing in salt water with an airstone running to form calcium carbonate and lower the pH, you will not get a dramatic rise in pH anymore when you turn off the airpump, which indicates that curing and leaching of K.W. and silicates are practically done and the rock is safe to use in a well aerated aquarium..
One more note on curing time. A few factors will affect the curing time of your cement rocks. For starters, small or flat rocks cure quicker. The pH of your tap water can speed or slow curing. My tapwater is about 7.6 to 8.0 pH and is high in calcium, magnesium and other elements that make water "hard". I get quicker curing times in this tapwater than people using soft water or R.O. water. Soft water with a low pH and with very low amounts of these dissolved solids will actually take longer to cure. Some people have even reported six months of curing in very soft or R.O. water! I suspect that you might not get the pH rebound with saltwater after a complete curing in R.O. water, but have not been able to verify this (yet).
Different materials take longer to cure also. Silica sand cement seems to cure faster, while aragonite cement cures a bit slower and crushed oyster shell cement even a bit slower than that. I still like the oyster shell cement best. It is cheap and has great porous texture.
No matter what method you use to cure your cement rocks, be sure to test the rocks in stagnant water for a few days to verify that the pH is not rising dangerously. WE are working on another accelerated (and SAFE) method for curing cement rocks and will pass it on to others and you if it works out.
When the rock has cured the PH should be 8.3 or under, correct?
Yes, but you can get away with slightly higher, but I prefer below 8, and even 7.5 to 7.7 holding steady in stagnat water for four days or longer (in salt water) for really cured cement rock. But, you can get away with just the freshwater cure and make sure you have good aeration to keep the pH down. You will see the KH in your tank or curing container of saltwater climb if the rock is still leaching. People do vary it a little, but the aragonite sand can get crystalized a bit with calcite even if it does not clump, so if you like the benefits of aragonite sand buffering and adding calcium, then be cautious on this point of jumping the gun.
Why are oyster shells a great substrate if they are high in phosphate?
They are high in phosphate and have silicates too, but others and I have not had a leaching problem once they are cured in cement.
How does the porosity of cement rock compare with natural rock? Have any measurements been made?
Some of my oyster shell rock is more porous than most wild rock. But, you can vary this as you like. The oyster shell is what makes it so easy to get the minor air pockets all over that allow tap water to run right through.
Any recomendations for better colors besides the dull grey concrete?
Yeh, but it costs... You can use white Riverside cement rather than the regular (and much cheaper) grey Portland cement. But I find that white live rock undersides eventually turn about the same color as the Portland cement anyway.
When will Coraline algae start to grow on new liverocks? Also what does Coraline algae looks like (shape, size, color) when it first appears on the rock?
Coraline algae starts growing immediately if spores are floating around in your water. You will see them after about 7 to 10 days of the new rock being in your tank if conditions are good - little pink, purple spots.
Do some polyps or corals attach faster to the rock?
It has worked well for me with any coral polyps I have tried with other rocks. I have made small cookies or blobs in the sand molding bed and then I can use these to attach corals to.
Concrete has capillary porosity. Since only the outside of the rocks isn't covered in concrete, how can these rocks sustain comparable amounts of bacteria?
I suppose if you make your rocks too solid or with not enough water or pourous holes from using oyster shell ... that you could have less bacteria .G.A.R.F. has had good luck with one of their tanks with 90% cement rock, but hey do not have a 100% one yet, but I don't think that matters.Jake Levi is the only person I know of with tanks with 100% cement rock and he says they do well. Others might have them too?
If you are adding cured rock do you discourage adding K.W. as a safety precaution?
Yes, I would discourage adding extra K.W. since you could get a minor leaching from the rock for a little while and if you only cure your cement rocks in fresh water and don't do a "saltwater follow-up" then you will get a K.W. spike when you put the cured cement rocks in to your saltwater aquarium.
Do you get the same amount of coraline growth on the homemade rock compared to natural rock?
Yes, I do, if I don't include coraline eating hermits with them. If your numbers of coraline eating hermits in your tank are low, then it just takes a lot longer for the coraline to get a foothold and grow - probably the hardier slow growing varieties that are not as tasty?
But if your numbers of these hermits are high, then you will really have a long wait to see much coraline growth.
My biggest question is, simply, why?
First, you can gain nice porousity with cement using the technique listed here. Any life in the live rock that will not reproduce and spread to your new cement rock will eventually die and be gone anyway, so if this was really a problem then you would have to change your wild live rock all the time! YOU DO however need to use a small amount natural live rock to provide seed material for these new "dead" rocks or they will remain that way! It is very easy to do this almost without trying.
