From everything I've read in the last 7 minutes
it seems as though it can be poisonous to fish at very high levels/concentration, same as melafix, I read how someone even put a bunch if eu leaves in their tank and it made more if a mess than hurt fish.. In my (no where near professional) opinion.. You're ok.. Assuming you keep up on water changes..if you start to notice a slick or film in the top of water than maybe time to reconsider??