1) Bottom dwelling fishes tend to tolerate Fish TB (Mycobacteria species) better than upper level fishes. The bottom dwelling fishes can get TB but they don't seem to develop the same symptoms or die as quickly as upper level fish. Presumably this is because they live on or near the bottom and are more likely to pick it up, so they have had more time to adapt and evolve with it.
2) The Mycobacteria grows slowly and will kill one fish here and one fish there. It's not like most diseases where you lose a bunch of fish over a couple of days and that's it. The bacteria grow inside the fish and over a course of months or years (depending on the size of the fish) they slowly destroy one or more of the fish's internal organs. When an organ is severely damaged, the fish suffers from internal organ failure and dies within 24-48 hours.
Common symptoms of Mycobacteria infection include sudden bloating (getting fat overnight), breathing heavily at the surface or near a filter outlet, stop eating, do a stringy white poop, die within 24-48 hours of showing these symptoms.
3) The pH has absolutely nothing to do with Fish TB and if people online are saying it does, they don't know anything about the disease. It can live in fresh, brackish and salt water fishes and the pH of the water can be anywhere from 4.0 to 9.0. Because the bacteria grows inside the fish, it is unaffected by pH due to the fish regulating the pH of their body.
4) Fish TB doesn't normally cause fish to lose weight. If the fish are losing weight over a period of months, they probably have intestinal worms, which are extremely common in fish like swordtails, platies, mollies and guppies that come from Asia. If the fish lose weight rapidly (over a couple of weeks), it's usually an internal protozoan infection. I would start by treating them for thread worms first, then tapeworm.
See the following link for treating internal protozoan infections and intestinal worms in fish.
Fish do a stringy white poop for several reasons. 1) Internal Bacterial Infections causes the fish to stop eating, swell up like a balloon, breath heavily at the surface or near a filter outlet, do stringy white poop, and die within 24-48 hours of showing these symptoms. This cannot normally be...
www.fishforums.net