Actually I have read on a quite a few sites that bleach is completely safe for freshwater tanks. Even plants can generally hold their own, but it doesn't bother fish not one bit. Granted you don't use too much.
yeah bleach is safe, use a diluted solution. make sure to rinse it very well unless you have a sodium thiosulfate solution to neutralize the bleach. we use it at the aquarium.
a hydra is like a jellyfish for freshwater (i had to do a report on it) but they can kill your little fish and hurt the big one but they look like a tree with four arms
