I have a female swordtail that suddenly is having trouble swimming up. No injuries that I can see. The tank is 36 gallon 0 ammonia. 0 nitrite, 20-40 nitrate (trying to fix it), temperature is 76-78. There is one other swordtail, 3 platies, 2 albino corydoras, 3 green corydoras aeneus, a bolivian ram, a bristlenose pleco,cand a gourami. I’ve had the swordtail about 2-3 months. What happened to it? Swim bladder disease?