The reason I think it's fin rot is that they have white on the edges of their tails and because you have a lot of aeration which can help with filtration in a way. One of the causes of fin rot is filtration is too strong that's why I say this.
you can't have too much oxygen in the tankCan you send a picture? It might be too much oxygen in the tank.
I do water changes about every 2 months. I did one about a month ago and i did 50% cause I was overdue by a month in getting it done. When I do those everything gets cleaned, gravel, glass, scrub down excess algae. I do the filter when it tells me to, whenever it turns red. I did a deeper cleaning on it when I did the last water change because it had some crazy algae growth that I didn’t like. It’s been fine since then.you can't have too much oxygen in the tank
Pictures of the fish?
How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do a water change?
What sort of filter is on the tank?
How often and how do you clean the filter?
What is the ammonia, nitrite, nitrate and pH of the tank water?
To treat white spot with heat, you need to raise the water temperature to 30C (86F) and keep it there for 2 weeks or at least 1 week after all the white spots have gone from the fish.
Did you use a chemical to treat the fish for white spot?
If yes, what chemical?
If the fish have a cream/ white film over their body or fins, it is excess mucous caused by something in the water irritating the fish.
Wipe the inside of the glass down with a clean fish sponge.
Do a 75% water change and gravel clean the substrate every day for a week. The water changes and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.
Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use them. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens.