What you are trying to do is replace/ dissipate the flea powder in the water. The only way to do that is too keep doing large water changes in the 75 % range. Then test, you may have to recycle your tank over again the flea powder killing your Benefical bacteria in the water. You need to test for Ammonia, PH, niTRITE, and nitrATE, You'll need an API LIQUID Test kit. This may be the only way to save your fish. Has anyone died? Have you locked your flea powder up? and you may want to lock up your fish cabinet as well. Kids love to dump the entire can of food.
Fish in Cycling