Betta fins look weird

[Namine]

Ok so update: Just got home from work. Betta still swimming like his back end is crippled. Honestly its looking more and more like his tail is fusing together if that makes any sense at all. Its collecting into thinkened parts at the fold and he swims like he cant open it and just kinda shuffles his butt side to side till he gets to another leaf to lay down. No interest in dinner. What would cause this?? I'm absolutely stumped here. I'm gonna change half the tank water and give him spring water with only prime in it nothing else. And I'll retest but all I have at home is ph and ammonia. I can take a sample to the pet store again this weekend. As for the platty with the white tail speck this morning it is now totally gone?? How long does it take ick to get out of a cyst? Could it even happen that fast? It did look like a white grain of salt at 7am today so it's been 12ish hours. Water temp still 78. The prime says it temp neutralizes ammonia and internet said that it remains effective 24 hours so I'll change half incase my test is wrong and add prime for now. What else can I do for him?? Does anyone have any idea why this is happening to his tail?? I see no fungus, his color is clear, it just looks more and more fused at the ends. The only thing I can think of is he does rest on the filter intake sometimes. Its openings are very narrow slits and I can't really cover it easily because its inside the back wall but he would swim up to it before this and stretch his fins wide and let himself get pulled up to it. I had panicked the first time put his fins didnt look pulled in at all and he would decide he was done and very easily swim away when I came over or there was food. Could it cause anything that would make his fins fuse? I see no tears or anything it just looks clumpy at the ends. Pics 1 and 3 show the ends best. When he moves he moves like his whole back tail is stiff.

 

[Colin_T]

The fish in the pictures looks like it has a white film on the edge of the tail and fins. Is that actually the case or is it the pictures?

A white film/ edge to the fins and or on the body is normally excess mucous that is caused by poor water quality or something in the water irritating the fish (chemicals or external protozoan parasites).

Check your water quality and do a 75% water change and gravel clean the substrate every day for a week and see if it helps. If it doesn't then it's probably protozoan and salt might help.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

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If you can post a short video of the fish swimming it might provide more info.

I don't know what else has been written, I can't read anything these days.