Rainbow fish swimming in circles

Wanting some other opinions on what could be going on here

A couple of days ago one of my turquoise rainbow fish started swimming in circles like this, for hours on end. Water test is normal for this tank, 0 ammonia 0 nitrite and about 30ppm nitrate.

I took him out, added him to a hospital tank with stress relief and then a few hours later added him back to the main tank. He wasn’t circling all day yesterday and then I woke up this morning to him doing it again. Thoughts?

I’ve read that whirling disease cannot survive tropical temps but I’m at a loss for what could cause this.

Small bit of backstory on the tank - I purchased this 75 gallon with the rainbow fish already in it in November. There were 3 large turquoise rainbow fish and one doritys rainbow fish the same size. I know they need larger schools so about two weeks ago I added 4 small turquoise rainbow fish.

I did remove the doritys when I removed the circling fish in case it was bullying due to being by himself, but these fish have lived together for 4 years before coming to me, and now he’s circling again so I don’t think it was that.