White patches on fins?

[aemaki09]

Hey everyone! I have been treating my main sorority tank for columnaris for about 2 weeks now with maracyn plus first and then furan 2 the second round, which ended this past Thursday. The columnaris seems to have cleared up, I havent noticed it on anyone in the past few days, but I am seeing these white patches on 3 different girls fins. All 3 of them have cello-type fins if that has to do with anything. None of these 3 had any signs of columnaris at any time, but I treated the entire tank so why didn't the medication work for this? It isnt fuzzy and its too big to be Ich from what I've read, but I have zero experience with ich at the same time.
one of the girls has it on her anal fin and it almost looks like it is melting at the end. I couldnt get a clear picture of her, but was able to get one of one of the others.

Anyways, if anyone has any idea what this is please let me know what it is and how I can treat.

Housing
What size is your tank? 26 gallons
What temperature is your tank? 81*
Does your tank have a filter? yes, aquaclear 50
Does your tank have an air stone or other type of aeration? no just what the filter gives off
Is your tank heated? yes
What tank mates does your betta fish live with? 6 female bettas 5 corydoras, and a few endlers as temp housing.

Food
What type of food do you feed your betta fish? Mix between NLS and Attisons and Attisons Pro for the bettas, omega one tropical for the endlers, and API bottom feeder pellets for cories.
How often do you feed your betta fish? 2x per day. amount varies.

Maintenance
How often do you perform a water change? 2x/week usually, right now been doing it 3+
What percentage of the water do you change when you perform a water change? 25-40%, just depends on the day
What type of additives do you add to the water when you perform a water change? Tetra Aquasafe

Water Parameters:
Have you tested your water? If so, what are the following parameters?

Ammonia: 0
Nitrite: 0
Nitrate: 10
pH: 7.8
Hardness: 11
Alkalinity: 9

Symptoms and Treatment
How has your betta fish's appearance changed? white spots on fins
How has your betta fish's behavior changed? hasn't
When did you start noticing the symptoms? its been a while, but figured the columnaris treatments would have worked on these symptoms so I didnt worry too much about it
Have you started treating your fish? If so, how? Not yet, just finished with a round of Furan-2 Thursday though.
Does your fish have any history of being ill? not since I've had them
How old is your fish (approximately)? 2 are about 4 months, the 3rd is probably about 6-8 months.

[ARNOLDluvsYOU]

To me it looks like your fish has Ich. its formed by parasites in the fishes skin. to cure your fish of Ich you should bring its water tempurater to 90F or 32C and you should add some salt to the water. You must also clean the tank once or twice a day. If this goes untreated then your betta can pass away. You should emidietly change your water and scrub the tank very well.you can also buy medication, but first do what i told you and if nothing happens in 2 weeks start using the medication.

[aemaki09]

isnt it too big to be ich?