Hello all. I have a 20gal tank that's fairly new (3 or 4 weeks old). Started off with LFS water (from their fish tanks, so it had bacteria in it already). We had 4 Halequin Rasboras, 5 Cardinal Tetras, 3 mystery snails, 1 ghost shrimp, 4 dalmation mollies, and 4 guppies. We returned a few mollies (didn't realize we had 1 male and 3 female to begin with and have now all females) and returned all guppies (due to aggression with the rest of the tank) a week after getting them. Then, the ghost shrimp died overnight of getting it. And now all Harlequins and Cardinals have died (one by one, about one every other day or so). So we now only have 4 mollies (3 dalmation and one yellow one) and 5 fry that one molly had a few days after we got it. We still have all 3 snails, too. Here's the issue: 3 of the mollies (2 dalmation and the yellow one) and all of the fry seem fine. One of the dalmations we are pretty sure is pregnant again/still but about to give birth (so we just separated it into a breeder net inside the tank last night since it seems boxy/ready to give birth). One of the other dalmation mollies though, have recently (last couple days) had a really bad curved back and is looking thinner and thinner. We've been advised from LFS (who had over 20+ years experience with fish tanks of both freshwater and saltwater) to only feed once per week due to our perimeters in the tank. When testing every week, our phosphates are super high/dark, Nitrates and Nitrates both high, but not super concerning according to LFS. We do a 30% water change every week and have changed the filter (Pura filter pad for phosphates and other stuff) about every 2 weeks. I'm wondering if the fish with the arched back has Fish TB or if it's just older? I'm seeing conflicting info online about both. If it is Fish TB that you think it is, I have cleaned the tank without gloves (new to this and never knew about Fish TB before this) and had hangnails on my hand. What is the likelihood of my catching Fish TB from that??? The fish in question does still swim around with lights on, and seems to be like the other mollies in behavior except the arched back and thinness. Any thoughts and tips would be appreciated!!!