Hello I've recently discovered aquarium fleas in my 40 gallon tank. They just keep multiplying. I know there not harmful to the fish but they don't look nice. I want to get rid of them. I've researched and have done water changes, zucchini in The tank, and blow dryer method. None nearly put a dent in the fleas. Does anyone have advice to rid of these critters? The little dark spots are the fleas, I think that's what they are?? Please help!