First of all, thank you for helping my poor fish. I am new to aquarium keeping, my only previous experience keeping a betta in a bowl for the past year. We got our kids a new 10 gallon aquarium kit for Christmas, and I was going to let it cycle for a couple of weeks empty, until I read that it needs fish in it to build up the good bacteria. So, we put the betta in it with some hairgrass and a plastic cave, then wanted it to look less empty, and did an hour of online research with no real conclusion. Newbies that we were, we went to Petsmart thinking to ask a "fish expert" there, and got two black mollies and two otos on the advice of the clerk that they were all compatible, as well as some live plant bulbs.
A couple of days ago, one of the black mollies developed white patches that I think are fungus, clamped fins, shimmies, and has been pretty much residing on the bottom of the tank. I've been doing 2 gal water changes every two to three days, complete with water conditioners, but yesterday I added 1 tablespoon aquarium salt, a water heater (which I found out when I brought it home does not allow adjustments, but keeps the water at 78, and then a fungus clear fizz tab. The mollie does seem to be doing a bit better, swimming around more and not much shimmying, the white patches appearing to diminish, though when I used my new test strips last night the nitrite was high at 3.0. Alk was 40, Nitrate was <20, hardness was 75, and pH was 6.8.
After doing hours of online research (stupid me for relying on a Petsmart clerk to know what fish would truly be compatible-she said she had all of them together in her two gallon tank at home!), I am still confused as to whether the fish can live together, and what to do about it. I have the following questions: (1)Will all of the fish do well with salt added to the water, and how much should I add? I am mainly concerned about the otos, since I found conflicting answers about whether they and the mollies could live with salt or not. (2)Do I need to do water changes more frequently until the nitrite goes down (say every day)? (3)The fungus fizz tablet from jungle labs says I can readminister in four days. How does changing the water affect this timeline? (4)I also purchased ammonia clear from jungle labs, but I am uncertain whether I should use it, as it sounded like it was similar to the water conditioner I was already using(Start Right from Jungle Labs). (5) Should I get some ick treatment and use it as well? The package said to use at half strength for scaleless fish, which I gather the otos are. (6) Should I be concerned about any of the water quality levels, and what can I do about it? I've been told the mollies like the pH much higher than the otos, and really have no clue about the betta.
All in all, what should my next steps be? Personally, I don't much like the black mollies after having them a week, but I don't want to just let them suffer and die, either. The betta is the fish we're most attached to, since we've had him for a year, so he is the one I would like to build the tank around (better job this time, I hope), though with the expected lifespan, he won't be around for much more than a year. We do have an extra 5 gallon tank, but no filter (or place to put it!) I do think the otos are cute.
Again, I thank you, and my fish thank you.