With such a big bioload, and weak filter, you need to be doing more waterchanges. From what you say now, i think its fin rot due to bad water. Like haychinook said, you might want to upgrade to a bigger tank, and get a better filter, also do some more water changes, like 2 per week 30-50% each w/c.rivendel;2681058; said:once a week... i just use aquasafe water conditioner...