My water levels were off due to a recent water and filter cartridge change, my local aquarium store told me to add stress coat, flakes to speed up the bacteria, and ammonia tablets. The store associate also informed me that I can give my fish fresh vegetable treats, any green vegetable like broccoli or peas. So I added the treatments, flakes, and crushed up broccoli florets ( just a pinch of it) about 6 hours later, this white stringy stuff started growing on all the decorations, gravel, and plants. Prior to adding anything to the tank, my water was clear and fish were fine, very active. Now they are at the bottom of the tank and their colors are very dark. I attempted to get the stuff out of the tank, and the fish seemed to become a bit active again and started eating the remaining stuff that was floating. 10 minutes later the stuff starts to grow again. What is this stuff? Can it harm my fish? How can I get rid of it? Please help....thank u!