Mysterious Molly Disease?
I am an amateur fishtank enthusiast who finally stopped moving every year so I could get a good-sized 49-gallon tank for some easy-going freshwater friends. I have had the tank for roughly 9 months. It holds about 8 guppies, 3 neon tetra, 1 pearl gourami, a bristle nose pleco, 2 dwarf loaches, and until recently, 4 mollies.
The past four months, my mollies have slowly one by one individually started swimming at an upwards angle with more difficulty. As each is impacted, I check the water parameters, watch them during feeding, and try to keep an eye on other fish. I do not have a Q-tank so it is important I notice if ANYONE is sick so I can treat the whole tank.
At first, months ago, it was one of my older mollies exhibiting signs so I didn't fret as they lost appetite and kind of wobbled in their swimming. They passed. No one else exhibited any signs in the tank of disease. The molly impacted also had no signs of discoloration nor raised scales or change in appetite. As they worsened, they seemed to have difficulty remaining stable in their swimming but never completely flipping over or being immobile. They also developed clamped fins. When the first passed, I was sad but assumed it was a fluke/old age. Two weeks later, I notice another molly showing signs of the same thing... she lasted about 3 weeks slowly worsening. No one else exhibited signs. She passed. I was now worried I had a parasite in the tank that was hopping from fish to fish. When I noticed my next mollie showing symptoms I acted a bit preemptively and euthanized them, hoping to nip the rotating 'whatever' it was in the butt. I did feel extremely bad about it, but this was after a round of fungal tank treatment, and I was going on a previously planned vacation where no one would be around to watch for them passing day to day.
My last molly has started displaying the same symptoms (weeks after the loss of the previous one). And I'm just not sure what to do?? It doesn't seem to be impacting the rest of my tank at all! Guppies and Gourami are happy and healthy and I'm still observing little to no visible signs of disease in the mollies. The only reason I'm catching warning signs is that I've seen three pass this way slowly over a month of changed appetite and slightly changed swimming/clamped fins. All of the mollies have been different colors (orange, gold dust, white, and full black) I've not noticed anything changing i their skin or color as they go through this process.
My tank parameters aren't exact as I use a dip test kit for now, but I have no ammonia, no chorine, no nitrites and minimal nitrates. I do weekly 25/30% gravel sucking water changes like clockwork and do add a bit of salt every other week to the tank.
Thoughts? I'd love to get more mollies, but not if I'm just slowly murdering them. I feel so responsible for failing these little creatures. It seems odd to me to be fish-specific as most of the time if there has been an imbalance and unhealthy tank, my guppies tend to be the first impacted.
Thank you in advance for reading this novel and any help you can provide.