Help!

Help!
[HR][/HR]I came home from school today and found a a bad sight. When I left in the morning my betta Spartan seemed fine. When I came home he was behind the heater, I know he wasn't stuck because he usually swims behind it. He was laying on his side but his fins were moving and when I went to get him out with the net to check on him he swam right behind the heater. After looking at him I think he might have fin rot but I didn't really realize it before because of his coloring. Hes breathing slowly, and I do see his fins going but he for the most part wont swim on his own. Please help, I really don't want to loose him. My other betta is doing well and acting active and normal.

These are the best photos I could get. His tail is a whitish see through until it gets to this weird pinky looking color that looks like it has mauve dots on it. I just cleaned out his tank yesterday a aprox. 97%

the only other tank mate in his tank is a mystery snail. I just cleaned the water yesterday so I don't think there would really be a harmfull fluctuation in water peramiters but ill try to test it tonight. Hes living in a 2.5 gallon (this was suppose to be temporary since I was planning on moving him into my 40 gallon because I thought my black moor was going to pass away and he hasn't wich im glad but now I cant use the tank so im hopefully going to get a 10 gallon soon to put my black moor in)
anyways my bettas tank dosnt have a filter yet because like I said I thought his stay would be temporary im hopefully going to get one this weekend. There is a semi sharp plant in there but there sharp parts are very small and its been in the tank for about 3 days but I now this isn't related to the plant because remembering nowa few of his fins were alittle ragady before I put the plant in (a fake plant). At the time I guess I didn't really think as much about it beause im 90% sure that I had a hydrogen sulfide water isuea (only in the tank) and his fins were alitlle read already from that.
Up until now hes been for the most part active and healthy as far as I can tell, but suddenly he just got sick. I added a sprinkle of aquarium salt and a drop of malifix and it seems to be helping some as hes swimming on his own every once and awhile. His breathing is still alittle slow and ive noticed that when he stops moving he tilts upword.
Should I keep him on malafix for the rest of the week (as it says to on the bottle) and use aquarium salt with 50% water changes and keep that up every day for a whole week?

Im sorry if my writing was confusing.

Well I know that the 10 gallon would be small but I thought a lot about it and I think he would do beter in the 10 gallon. theres nothing else in the 40 gallon there was just snails but those are in my 50 gallon because I was medicating my 40.
unfortunetly last night both my betta and my black moor passed away.