female balloon molly acting strange

Question
Hello,
 I would like to start with the fact that we just got a fish tank as a complete  hobby, I used to have a large tank when I was 14 and it had sward tail and guppies in it, however in this new tank we got we have 2 male guppies, 3 female mollies, 1 sward tail and 2 balloon mollies. The tank is 20 gallons. We check the water quality and it is all normal. I am not sure what filtration we have because my husband is the one taking care of it but I know we have a regular filter I think and then air pump. At first all fish were ok, then we noticed that our mail sward tail got fuzzy around his mouth so we got medicine, we followed the directions and then his fuzzy was gone, but he died anyways, we had a female swardtail that died too- nothing visible on her, then one of the regular mollies had a problem with her eyes they popped out but after the medicine was in the water her eyes went back to normal, all that happen like 1 week ago. Since we put the medicine in the water and did the water change my female balloon molly has been acting strange, she does not swim around just stays on the bottom, when we feed them she comes out to eat but swims kind of nor coordinated, like the other fish can move her around, then after she eats she goes back to the corner of the tank and stays there, she moves away when I tap on the tank wall, and in general swims around from time to time, but she looks sick to me, her belly looks a little strange in shape like a square like a female guppy would look like when pregnant, so I can not tell if she is pregnant also a friend of mine said she looks like she is missing one of her thins on the belly which i can not see, because compared to the mail she looks the same just smaller, Not sure what is wrong with her, is there any way to help her, do you think she has a bacterial infection, not sure if the rest of the fish and her problems are connected or is it just her. The rest of the fish seems to be good, the female sward tail likes to stay in the corners but looks normal i think it is just because the male guppies have been chasing her around, they used to chase the female molly too but now no other fish bothers her. Anyways if you have any idea what could be the problem with her it will be greatly appreciated. We also have 2 very young may be 2 weeks old guppy babies in a separate part of the same fish tank and they are doing great. Again the total of fish right now is 8 adults and 2 babies.
Thank you very much

Answer
Hi Gerie,
Sorry to hear about the problems you've been having with your fish!

The mouth fungus and 'pop-eye' are typically bacterial/fungal infections that attack sensitive livebearing fish such as mollies and swordtails when they are either stressed and/or the gravel is not vacuumed and water is not changed enough to keep the environment less inviting for infectious bacteria or fungi to develop.

It really sounds like the female balloon molly is pregnant and may be very close to having her babies. Her appearance and the symptoms you described really point towards that. I would hope she is not coming down with an illness. Just keep an eye on her as you have been already.

Remember, all the medicine added puts additional stress on your fish. So not only are they dealing with any possible illness occuring... they are also stressed by the chemicals in the medication itself. Plus many medications destroy the good bacteria that live in the gravel bed and filter. These bacteria are known as your 'biofilter' -- the creatures that keep ammonia produced by the fish at bay. Without them, the tank water can quickly become toxic and even deadly if partial water changes are not done to dilute the ammonia as much as possible like during medication treatment for example.

This is a very important thing to keep in mind whenever you have to medicate your fish.
Partial (30-50%) water changes are the key. Make sure to always add water conditioner and try to match the temp to the original tank's temp or just a little bit warmer.

Your Balloon molly may simply be about to have babies. To be on the safe side, I would do a couple of 30-50% water changes on the tank to insure its not a water quality issue.

I hope this helps and good luck!
Susan~