1. It is grey/white it is really hard to tell has there is black spots as well and his natural color is still somewhat there.
2. It came really quickly, I started noticing a week ago. It started with just a strip and now it's his whole dorsal fin.
3. It doesn't really look fuzzy, no.
4. It was really hot that day, 26 degrees C outside which makes the house hot, it has lowered since then.
5. I only added aquarium salt on Saturday after a water change - another user told me to stop until I knew what was wrong. I used what the box told me to. I added half a tablespoon for my 3.5 gallon tank.
6. Just the one day.
7. No change in behavior whatsoever, still swims, eats, and everything.
8. All his other fins are fine, just where the dorsal meets the body is also starting to turn white/grey.
AQ salt in this case could be used as a preventative for further bacteria protection, but I don't think it will do much for him since his behavior hasn't changed or anything. It is an odd change of color, but maybe it is natural and just hasn't colored up complete yet? Sorry, just shooting things out and hoping they make sense lol.
I am just thinking if it good idea just to stop aq salt since it not even therapeutic dose and will not help any way. It just better if Lissa will use when she really need it. And since you can't use it all the time and also immune system can get resistant to it may be it just better to stop, especially if he don't have any behavior changes and acting the same ?
Bettas are sensitive to aquarium salt. I would not use it unless there was a specific need for it. Aquarium salt contains sodium, which puts stress on the kidneys, and can lead to fluid retention and bloating. (This in turn, can lead to other problems.)
It's not that the fish's immune system will get used to the salt. (It won't.) The concern is that the *bacteria* may become resistant to it. If they do, then harsher chemicals are needed to destroy them, which in turn puts additional stress on the fish's internal organs, etc.....
I'm a big believer in watch closely, and wait. If the fish continues to behave normally, then life happily continues. If something changes and there's a clear sign of infection or disease, then I would begin some kind of treatment.
I also want to make sure you remove all debris from the bottom of the tank , under the gravel . Are you using siphon to do it? And if your filter "all-in-one" cartridge that is filter floss with carbon inside, just rinse it once a week in tank water or dechlorinated water. Most of the filters use those kind of cartridges. If the cartridge becomes too old or starts to fall apart, put a new cartridge in the filter but keep the old one behind it for a week and monitor for ammonia spikes.