[Maleficent]

So I've had my boy Blue since October 6th so a little over a month and he was doing perfectly fine until about a week ago when I was able to get a siphon to clean the gravel(before that I just used a cup for water changes). The gravel had a lot of waste in it and the next day the nitrite and nirate levels were off the charts high and I tried for about 4 days to lower them but with no luck. I started noticing his fins were fraying when the levels spiked and it was getting worse and the water wasn't improving. I did research and decided it was fin rot. While at the pet store to get medication for it I also got a larger tank because I only had a 1.5 gallon(filter and heater) and during research I realized I needed at least a 5 gallon. So I got him a 5 gallon tank(filter and heater) and Seachem Stability for a new tank. They said it would be fine to mix the Stability with the meds so he's been in the new tank for 4 days and I did use a water conditioner and have been testing the water daily. I got API fin and body cure and I also got salt too. I'm on day 4 the last dose of the fin and body and I'm not sure what signs I should be looking for that he's getting better or how long I should wait before dosing again if he doesn't show signs of improvement. I'm not even sure if it is fin rot. I read it could also be columnaris. He's got sort of a white spot on his head. I'm not sure if it's always been there but it's not fuzzy. I'll post pictures of how he looked when I got him, at about 2 weeks and then how he looks now. Help would be most appreciated.

Housing:
How many gallons is your tank? 5
Does it have a filter? Yes
Does it have a heater? Yes
What temperature is your tank? 79
Does your tank have an air stone or other type of aeration? No
Does your Betta have tank mates? What kind? None

Food:
What food brand do you use? Tetra Bettamin Flake Medley but just switched to Ultra Fresh Betta Pro Shrimp Patties 2 days ago.
Do you feed flakes or pellets? Pellets now
Freeze-dried? No
How often do you feed your Betta? How much? 3-5 pellets twice daily

Maintenance:
Before your Betta became ill how often did you perform a water change? Once a week
What percentage of water did you change? 25%
Do you vacuum the substrate or just dip out water? Vacuum gravel now
What additives do you use? Stability. Prime and API tap water conditioner

Water Parameters:
What are your water parameters? Please give exact numbers. If tested by pet store please get exact numbers. "Fine" or "Safe" won't help us help you.

Ammonia: ?
Nitrite: 0.5
Nitrate: 0
pH: <6.2
Hardness (GH): 25ish
Alkalinity: 0
(KH): Carbonate 40

Symptoms and Treatment:
When did you first notice the symptoms? 8 days ago

How has your Betta’s appearance changed? Tail is frayed and ragged and missing pieces

How has your Betta’s behavior changed? He hides more now

Is your Betta still eating? Yes

Have you started treating your Betta? Yes with API fin and body cure I just gave the last dose(day 4) and 1tbs of salt per 2 gallons