I noticed on Saturday that one of my Buenos Aires Tetras has swollen gills. I have a 40g tank with 6 BA Tetras and 4 Corys. The tetra is not acting sick, she is active with the other fish and seems to be interested in eating (I haven't actually seen her eat because the back of my tank is a little dark). She is not struggling to breathe and has no other signs of disease. No one else is showing any signs of disease either. I haven't done anything new to the tank. I've had all the fish for about 8 months and the tank itself is about 12 years old.
Anyway, I cleaned the tank on Sunday (this is my regular routine and I thought that the water quality might be the problem). Today, Tuesday, I checked and she still has swollen gills (the left side worse than the right). Other than that, everything else is the same. I ran water tests and ammonia = 0; nitrite = 0; ph = 7.6.
So, I'm trying to decide what to do. I've read that aquarium salt could help but is not good for the Corys. I'm afraid to medicate because I've never had good results in the past.
tank size (in gallons) - 40
how long in operation? - 12 yrs
total number, species and size of fish (or other aquatic life forms) - 6 Buenos Aires tretras, 2 bronze corydoras, 2 leopard corydoras
newest additions to the tank (including plants) - none
type of filtration - carbon filter
aeration - air pump w/ 2 3" round bubblers/stones
water additives ( conditioners/dechlorinator, Ph adjusters, salt or any other chemicals added) - use prime at water change, otherwise, nothing else
water change amount and frequency - every 2 weeks; 25 - 30% water change (same procedure for 12 yrs)
feeding...what, how much & how often - 2x/day; flakes & shrimp pellets in AM - blood worms in PM
unusual findings on the fish - just swollen gills; gills look a little red underneath
Behavioral problems (not eating, hiding, sluggish/lethargic, swimming problems, etc.) - none