2 Months Of Fin Rot??

Hi! A while back i I posted about my betta Nico who was suffering from fin rot. It took about a month, but he finally recovered and his fin was almost completely grown back. But then, about 4 or 5 days ago I noticed some red spots on the tips of his fins. I immediately did a water change with a bit of AQ salt in hope of preventing anymore damage. To no avail, it didn’t work, and now my poor bud has fin rot again This has been going on for 2 months now. I believe the first round was due to his tank being stuck mid-cycle (increasing ammonia, no nitrites or nitrates). I finally got it to break, and now his water is reading:
pH: 8.0
ammonia: >.25 (there is just the slightest hint of green)
nitrite: >.25 working on this, but again, tank was stuck in a cycle)
nitrate: 5 ppm

I just dont know what to do anymore! I did water changes every other day once his fins were close to grown back because of the water parameters, but now I’m back to daily changes and he’s just not improving. I don’t know if I should dose his tank with medication. If I should replace the filter (i clean it in aquarium water every other week). If I should just do a complete sweep of his tank and clean everything. I really want him to recover, and recover for longer than a few days, but I’m just completely at a loss now. Any information or guidance would be absolutely wonderful.

there’s also a black spot on his head that is not his normal color, but I’m pretty sure it’s just a bruise (he got really excited for food and jumped out of his tank a bit for it bc he just couldnt wait and accidentally hit my finger instead).

(here’s some pictures he wasn’t really in the mood for)

 

Are you using a dechlorinator to protect him from the ammonia & nitrites? (Prime or other)? How big is the tank? Could there be any rotting plants or food hidden in the gravel or underneath decorations? Sometimes fin rot requires an antibiotic, but I don’t have experience with that sorry.

 

I use Prime to condition his water and the tank is 5.5 gallons. There are no live plants (though i do plan on moving him into a planted 10 gallon over the next few months) and I make sure to clean the gravel regularly to get all food and debris out. I’ve done a lost of research since his fin rot initially started and have basically done everything but antibiotics (