Molly has the shimmies?

[B1gJ4k3]

A few weeks ago, I picked up 5 black mollies form my LFS and put them into a 75 gallon quarantine tank, along with some others. They seemed OK to start with, but eventually, I started losing them and they seemed to be having trouble swimming, kind of wiggling rapidly from side to side and some of them seemed to have some swim bladder issues because they would have trouble staying horizontal in the water. I moved them to their own 20 gallon quarantine tank, put some salt in, raised the temperature and fed peas (which I don't really think they ate). Two more died in the 20 gallon quarantine, so I went back to normal feeding and temperature, but now I'm down to only 2.

One seems OK. She seems to be breathing rather rapidly, but I don't know if that's just stress of me observing her. She's eating normally and is pretty active in the tank. The male, on the other hand, just doesn't seem right. He also breathes somewhat rapidly and also seems to have trouble swimming. He's got a little bit of the wiggle going on (which apparently is called "The Shimmies" or livebearer disease--although I'm not really sure that's the problem based on my water parameters below). His back also seems to be kind of weak and his tail is often either curved up or down and he spends most of his time either at the top or the bottom of the tank.

My water parameters are fine. No ammonia or nitrates, really for that matter. Hardness and buffer seem fine (although, that's admittedly an area I don't know much about). PH is buffered up to 7.6 with crushed corral in an HOB filter. Temperature is now 76ish.

I'm not really sure where to go from here. At some point, these two obviously bred because I have two little fry swimming around in a breeder net in the same tank. The rule usually seems to be "if they're breeding, they're healthy," but with livebearers, it's not terribly difficult to get them to breed.

What should be my course of action here? Do I treat the whole tank (including the fry) for something bacterial? Do I further isolate the male and see if it's a swim bladder issue with some epsom salt baths? Do I risk moving the fry and the female to my display tank? Given the history with the other three that died, is it just a genetic thing and he's a lost cause? Not sure where to go from here, so any advice would be much appreciated.

[Scapexghost]

My guess is the hardness and pH is the issue. Thats what usually causes shimming. Mollies also shimmy right before giving birth, so it the female was shimmying and is no longer shimmying, that would be a possible explanation. While those levels should be okay for mollies, or at least not instantly kill them, if they were raised in harder water or brackish water the shock could have killed them. It is also possible that you're water is very low in calcium and very high in magnesium, so while your water tests hard enough it may not be suitable for mollies. 

It does not appear to be a swim bladder issue. When mollies have swim bladder issues, they will swim at a 45° angle at the surface of the water and will not be able to right themselves. Swim bladder issues also wouldn't kill the mollies.

Regardless of the cause i would treat w/ one tablespoon of salt per gallon of water. Mollies are very salt tolerant so this doss will be less stressful than any med would be. If fact, it should relieve stress. It may already be too late for the male but this should give him the best odds of survival. 

My main focus would be on the fry. They have the best chance of adjusting to your water long term. I would keep them isolated until they are large enough to not be eaten by other fish. I wouldn't treat the fry with salt. They should spend their entire lives in the same water parameters, so match the parameters of whatever tank they are raised in to the display tank's.

[Colu]

It could low KH @Scapexghost suggested causing  these symptoms  low levels of minerals can cause shimmies in livebearers. aquarium salt will help with gill function and add essential electrolytes  it can also be cause by to low temperature or pH  these multiple factors that can cause shimmies

Edited October 7, 2021 by Colu

[quikv6]

I agree with the above. I have livebearers, and I believe a PH of 7.6 should be fine, but your KH is quite low, which can result in PH fluctuations. Crushed coral does work, but if you are doing large water changes, it takes time for the parameters to "catch up" , so to speak.

Here's what I do, since I have VERY soft water with low KH out of the tap.

1) Crushed coral in the substrate

2) Crushed coral in a HOB filter. (It dissolves faster due to the flow through it.)

3) Wondershell (for GH)...though your GH looks great.

4) Baking soda (BE CAREFUL if you go this route!) added to the water during a water change. This raises the KH/PH of the tap going in to match what is in there already. If you decide you want to try this, test (I repeat...test) a given amount of baking soda in a 5 gallon bucket first, to see exactly  what effect it has on the PH/KH. A given amount will have a different effect on different water.

I have found that 1/2 teaspoon per 5 gallons gets me from 6.8 to 7.6, and brings the KH from 40 or below to around 100. But that is on my water. Definitely test first.