Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Silica as in play or pool filter sands, some gravel and other sources is not a problem for fish or plants in an aquarium. It can trigger the growth of 'Brown Algae', also known as Diatoms. (Google for images, they are really interesting seen under a 'scope').
The secret is to remove the silica as fast as possible. Allow the diatoms to grow, they are filtering the silica out of the water and incorporating it into their body. If they are allowed to die in the tank that silica gets recycled into more diatoms.
If you remove the diatoms then the silica in their body gets removed. You can wipe off the diatoms from things you can remove from the tank, or you can get Otos or a few other fish to eat the diatoms, then vacuum the poop. Or you can wipe off the things while they are still in the tank, and keep the siphon close by to remove the diatoms.
Keep cleaning the filter media, too. Gently, the new bacteria are still colonizing it, but slosh the sponges around enough to remove the diatoms.
Even if you do not make any effort to remove the silica eventually the diatoms will die off. It just goes faster if you can keep on removing the silica.