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is cement toxic?


Sep 30, 2003
i was wondering if anybody knows weather cement (dried and hardened) is toxic in salt water, or could over time release toxins into the water?

i was wanting to try to make artificial caves and things the octo would enjoy checking out, i was going to use cement but then thought of the chemicals involved, although once hardened the chemicals might not release into the water.
Well all I can go on is our tanks, all of which are concrete! They seem to be fine (some are 73 years old!), but the concrete needs to cure before you add any stock. What we have done when remodelling is let the concrete dry then fill the tank and leave in the saltwater with no stock for a couple of weeks. Then drain let dry and refill then season/cycle as normal. Also you could check with your supplier about the reaction by the concrete to saltwater. They must have some idea, for homes next to the sea!


We use concrete mixes frequently for use in tank backrounds and to build artificial reef structures...but it is an involved process.
Use a premium grade portland cement. If you are going to be doing a lot of detail work, mix it 50/50 with plastic cement.
Once your work is done, set it aside to dry for 7-10 days. If you can get it outside after the first 36 hours, you will get a better cure.
Now comes the fun part. If it is a free-standing piece (seperate from the tank) you can soak it in a plastic container, if not you have to soak the entire tank. Fill whichever receptacle with tapwater and add 2 cups of muriatic acid (used for pools) per twenty gallons, being careful not to pour it directly onto the cement. Mix the solution and let the cement soak for three days. Drain, and repeat. Drain and rinse off thoroughly. Let stand to dry for 2-3 days. Don't freak out that the cement has turned brown...it is a normal reaction .
Fill the tank with r/o water and introduce some goldfish or the like to test and make sure you leached the concrete enough...if they live, go ahead and start your salt tank, or if it is a seperate piece, place it into your tank...
Sounds waaay more complex than it really is...let me know how it goes!
thanks for the info, very helpful.
im not making anything big, just small artificial caves for the octo to hide in, i have rock but it doesnt make a fully enclosed cave where the octo could feel safe in, there is a plastic shipwreck which is hollow but it will eventually be to small. i was going to put the artificial cave in the corner and cover it with caulerpa so detail on the cement is not an issue

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