Parasite???

Question
Hi, I asked a question to another expert from this website about my fish but when I wanted to ask a follow up question, my computer  told me she was unavailable. Maybe you can help? My molly's are acting VERY weird. They are shaking, laying around,and their fins are disappearing. I first asked the expert, but she was taking some time so I went to my fish store. They gave me pimafix and told me it will fix everything. I put it in yesterday and my fish seem to be doing better! But then the expert answered and told me I had a parasite.... she gave me meds to use- proform c. Should I use it or should I keep using the pimafix? Also, how many fish can I have, once my problem is fixed, in my tank? It is 50 gallons with 3 houses and has many plants. I also have 2 frogs and 2 crabs. This upcoming Friday I am getting a Farlowella Gracilis to clean my algae. Also, which fish do you think may be right for me? I go to school all day and will only be able to clean it on the weekends. I do feed them everyday and check my Ph levels and bacteria levels once a week. Thank you very much!

Answer
Megan,
If their fins are disappearing, that is fin rot. This is a problem that usually appears in water that is not the best quality. Maybe the ammonia and nitrites are up. Make sure you do water changes weekly.  Add some aquarium salt to their water and the ratio of 1 tablespoon per 5 gallons of water and make sure the heater is set to the right temperature. Since you have already started medication, it is best to let it run its course. As for the stocking of the tank, there are a lot of different types of fish. There are peaceful community fish, there are semi aggressive fish, and aggressive. There are bottom feeders, middle swimmers and top swimmers, salt and fresh water, cold and tropical. The best advice I can give is to research all the different types of aquarium fish. Find the one fish that you absolutely have to have and then let me know what that fish is and I can help you further.