Possible fin rot

[AlmonB]

Hi! I think my sunburst platy has fin rot. His tail fin is looking like its slowly deteriorating and his arm find are looking much smaller especially in comparison to my Mikey mouse platy. I've been researching on what to do including aquarium salt, melafax and water changes. I'm going to go to petsmart after work today. What do you recommend? I have 2 ghost shrimp, 2 male guppies about an inch long, 2 male platys. My tank is peaceful since I rehomed my danios. So I do not suspect bullying. My tank is a 20 gal. I just really don't want to lose my sunburst he was my first fish and I picked him myself! (Or any of my fish for that matter). All other tank mates look fine. So should i try melafax and aquarium salt along with water changes? Or are there other remedies?

 

[AlmonB]

By the way, my water readings are ammonia- 0, nitrites- 0, nitrates-5-10. My tank is at a constant 79F

 

[AlmonB]

Just gonna bump this with a little update. I did a 50% water change and I'm adding melafix. He is staying on the bottom but is swimming to eat.