Saturday, October 25, 2014

Styrofoam-cement aquarium background

I have mixed feelings about this project. At first the rock background looks fantastic. If your fish don't mind high pH, it is great. Now, the bad part is that it gets covered with algae really quickly and if you cannot keep enough plants, it may not look too good. We had Pete, the parrot cichlid in there, so plants were bound to be dug out. Therefore, we ended up getting rid of the background. This is the other drawback, since you silicone it to the tank, this means changing the fish tank. Thank goodness for $1 per gallon at Petco.

So, if you want a dramatic background, can have enough plants to limit the algae growth and have fish that tolerate higher pH values, here are the steps.

At first it seems like it is really complicated and that the chemistry of the water can be jacked up quite easily, but if you let the concrete cure for long enough and then rinse it for about a month, then you'd be fine.

First step, think about what you want your aquascape to look like. Then use styrofoam and silicone (make sure it is 100% silicone without mildew protection, as these chemicals would send your fish to heaven, provided they were good of course) to construct your dream. We used insulation foam from the hardware store (a lot cheaper than the foam at the crafts store).

 Check the fit for the filter!
Once we had this done, we made a very watery mix of concrete and applied it with a paintbrush on the styrofoam (hello Pookie!):

 We used standard hydraulic cement paint (the cure timing is lower than regular cement). Let this layer dry and apply a thicker coat. If I were to redo this project, I would force myself to apply 3 or 4 coats of concrete, as I was able to peel off some concrete when cleaning the tank later on. Don't make your layers too thick and spray water on the concrete regularly while it is curing. Otherwise, your concrete will crack when it cures. Don't apply a coat until the previous one is completely dry. Concrete takes a long time to cure (weeks). So, at least you want to wait a couple of days between layers. Once you are done, you can test fit again and then silicone the crud out of the back to attach it to the tank. Don't go stingy on the silicone now. You probably have gone through 10 - 15 tubes now, no reason to stop. If you go stingy, some pieces will float... you can ask my wife, the middle piece, that we called the fireplace, just took off and almost broke some lights. Let everything dry/cure for a week or more and pump the water in.

Now, you need to put a little circulation pump and a makeshift filter:

If you don't do this, you will end up with concrete on your glass and you will have had ruined a perfectly good fish tank. So, make sure you have the filter and circulation. Once a week for the next month or two, change all of the water of the tank. This tank is not fish safe yet. Once you read the pH of your water and it is not more than 0.2 higher than the tap water, you can throw in some substrate and for good measure, let the filter run for another week. This takes a lot of patience, I know, but you HAVE to do it.

You can see in these pictures that we set up the tank in the family room. It was intended for the living room, but there is too much mess going on when you do this, it is better to have your project in a hidden room.

When the time finally came we added the plants and the fish.
 After the fireplace floated away. We added a lot more plants there, to try to cover it up. That made Pete mad, and it was hard to keep the plants in place.
  If you have any questions about this project, please leave your questions in the comments section.

Happy building!


  1. Hi there i need your help please. I want to make my rocks look in red colour. What should i use? Can i use nirmal concrete cement for coating? Thank u. Appreciated. Singapore

  2. There is a coloring that you can mix into the cement mix. I would let any chemicals leach out for a while before putting in fish.

  3. I am currently making some rocks for an outdoor kitchen and am using Sakrete color. As I said, the only concern is to make sure to wash the chemicals out before putting fish in.