dying fish =(

Question
I'm not sure this is the problem anymore. This morning when i checked on the molly, sucker-fish and snail, they seemed to be fine. But this after noon when i got home from school , the molly was dead. I am getting annoyed. =( My mom said it looked like the dead fish were red all over under their skin. But the snail had this thing that looked like a cluster of a bunch of little red dots hanging off of it. Is there a way to make sure the last fish lives with the snail, or should i get rid of the snail? Or do you think there is a treatment I should give them? I hope they live!!!
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The text above is a follow-up to ...

-----Question-----
ok, so I have had these two fish, a smallish kind of cat fish, and a smallish kind of sucker-fish. I had the sucker-fish for at least a year and the cat fish for a LONG time. About a month ago we got two new male Dalmatian Mollies, and up until today, they've been fine. Ok, now it might get confusing. Just a few days ago, I got a brown mystery snail or something like that, and EVERYTHING seemed to be doing fine. And then this afternoon, my poor old catfish died, but I figured it was just because he was old. But then an hour later, I noticed one of the Mollies was now dead. I hadn't noticed anything suspicious, except the two Mollies were swimming stationary at the top for a little earlier today, but then stopped. So I put the remaining sucker-fish, 1 molly, and snail in a new tank. One thing I noticed, I don't know if this killed them, but there were tiny micro-organism like white things swimming on the dead fish. I don't know, maybe they're just decomposers? Please help! I should probably do a total clean of the whole tank, right? But do you have any suggestions that could help this situation, now or in the future, or just to always keep the tank parasite-free? And is there anything I should give the still living fish to assure they don't have the same fate? Thank you so much for giving your time to help me with my super confusing problem!
-----Answer-----
Hi Anna,
The worms you are describing are probably planaria. They are harmless and usually appear when you have too much uneaten food left in the substrate. If your mollies were at the top gasping for air this would probably be due to high ammonia levels. Is your tank cycled? If not this will explain why your fish died. If you would like anymore info please ask.

Regards,
Chloe.

Answer
Hi Anna,
Did you get your water readings checked? If not please do as this will rule out why your fish are dying. You must also separate the fish so they won't be able to catch anymore diseases. Move your snail to a quarantine tank and perform daily water changes and make sure he has a good diet of algae. If the fish has red under its skin it could be Inflammation all fish are open to this. When a fish is subjected to waste product buildup in the tank in which they reside they may show signs of inflammation. You can treat it by using an antibiotic such as nifurpirinol.

Good luck!
Chloe.