New betta has strange flickering transluscent eyes and possible SBD-- help!

[wyrmiii]

I got my new betta about 3 1/2 days ago, and he's been gaining strength over time,  but I bought him sick and I'm not entirely sure what diseases he has. He was in a cup that was full of poop and a relatively thick layer of algae, and struggles to swim upwards. I'm pretty sure he has swim bladder disease, though I'm not sure if it's from stress or something else. 

The main concern I have about him is actually his eyes-- I've tried looking up what could be wrong, but I'm not getting any results that seem like his situation. I don't know why he does this, but sometimes his eyes just go transparent; sometimes partially, sometimes fully, but always from his usual black to showing a fleshy pink like the inside of his head. I have absolutely no clue what this is, but I'm starting to worry its some kind of rare disease or something since absolutely nothing about it is showing up on Google.

If anyone can help, I'd be very appreciative-- I would also like a second opinion on the swim bladder disease diagnosis if possible, too 🙂

Here's a video of his eye changing color:

https://photos.app.goo.gl/JuzE9VuyDnUUipG5A

And here is a video of him trying to swim, also with his eye briefly changing color: 

https://photos.app.goo.gl/CUQAgT2RTBJ7Rs9R7

My tank is 5 gallons, fully cycled, with a filter and heater. Current parameters are 6.8 pH, 50ppm nitrates (I've been doing 15% water changes daily to bring this down), 0/0 for ammonia and nitrites, KH of 80mg/L and GH of 50mg/L. My TAL is also 90mg/L. It's been consistently at 78/80 degrees F, and I acclimated him before putting him in, but between the poor conditions in the store, 10 minute car ride home, and new environment alongside thunderstorms, I think he's still stressed too. 

 

Edited September 14, 2023 by wyrmiii

[Colu]

Could be swim bladder with what your describing and looking at the video for the swim bladder you would want do Epsom salt baths 1 table spoon for 2 gallons for no more than 15 minutes for 5 days as Epsom salt acts as a muscle relaxant to help relieve pressure on the swim bladder and for the eye issue I think it would be worthwhile doing a course of kanaplex that's a broad spectrum antibiotic treatment and an extra air stone during treatment @wyrmiii

[wyrmiii]

Thank you so much @Colu, this is a big help!