Does this look like fin rot?

[Steenie]

I attached a picture. The one on top is him about 2 weeks ago. The bottom two pictures are from today. I noticed his one back fin (caudal fin) worn away a little..could this be fin rot? (ps. you can see it better in the last picture) should i add some aquarium salt??
Also his fins have been getting darker since i first purchased him.
I've been adding 2 drops of prime to the water as it is a 1 gallon tank and doing 100% water changes weekly. Should I be doing more? I also have it heated but it only stays around 76 with the heater I bought :/

[callistra]

It does look like fin rot to me, yes.

1 gallon is okay for a temporary or hospital tank but 2 gallons is really minimum to keep a betta in long term, and bumping up to 5 gallon makes it a tons easier on that.

1 gallon tanks need a minimum of 2 water changes a week - one 50% and one 100%. Some people will even do a couple smaller changes followed by the 100%. Using prime will help keep the ammonia levels down in such a small bowl too. When you do a water change you can avoid shock by using the thermometer to get the tap running at the same temp as the water that you replaced from the bowl, but also cupping and floating the cup and acclimating him slowly by adding a few tablespoons of water to the cup every 10 minutes for an hour or so each time you do the changes, especially the 100% ones.

He needs to be a little warmer ideally, yes. Getting something larger will also help with that because at 2.5g + you can get good adjustable heaters.

Adding salt is okay at 1 tsp per gallon predissolved for up to 10 days. Whenever you make a water change, add as much salt as you take out.. so on the 50% change days add 1/2tsp pedissolved back in.

So.. he needs cleaner warmer water and ideally a size upgrade.

[Steenie]

Ok. I can increase the water changes then. I may have to wait a month for an upgrade in tank & heater though :/ But I could do the aquarium salt for a week too.