its not critical in the freshwater aquarium but in a planted aquarium its everything. I have a hudge diatom alge bloom beacuse there is too many silicates. I did a 50% water chage and it got worse thats why I tested my water. I have found that its high and now the diatom population doubled in my tank. so can I just put this stuff in my water change bucket over night to remove silicates. I can not put it in my filter because my tank needs phosphates for the plants.