This tank has been up and running for over 4yrs with that filter and never a problem. And NO there is NO ammonia or ANYTHING they could find in the water. IT was due to a stressed out ananome that decided to release her toxin into the tank I have taken her out, did massive waterchanges, carboned the hell out of tank and Denis is taking care of my fish until this problem is solved. But yes this filter may be small but it has run like this for a long time and I didn't add 30lbs of new LR it was 15lbs new LR I already had 15lbs of older LR from 4yrs ago in there