Last week my gar started having some seizures and went belly up but he then came back to. I thought it was some sort of gill parasite. I treated the tank for 4 days w/ tetracycline. I have a 120 gallon tank so I dosed it for 80 gallons to play it safe. Four days into treatment there was no sign of improvement so I did a 40 gallon w/c. My filter media was quite dirty. I normally do weekly 40 gallon w/c's. But I recently added 6 bichirs to the tank and I am now having to feed a bit more. Maybe it was the dirty tank that caused this problem????? Should I do 40 gallon(30%)w/c twice a week?