Possible illnesses

So I thought I kill two birds with one stone and put both my questions on different fish in one thread. I'm really not sure if these are illnesses, but they've got my attention and I'm curious if there's any input.

So first I have this harlequin rasbora. For close to a month now, I've noticed this white speck(my first instinct was ich) appear and disappear on my male harlequins lips. One day it will be on his lip, one day it won't be. It always appears on the same spot on his lip. The female harlies and the betta and corys have not had any parasites pop on them. Like I said it's been going on off and on for close to a month now. No one gets sick , no more spots appear anywhere else on the male harlie, just his lip. I netted the harlie one time while he had the spot on his lip and pulled him out of the water to inspect him and he flopped out of the net and back into the water and when I looked in the tank the spot was gone. It honestly looked too big to be ich, It crossed my mind that maybe he was carrying a piece of sand in his mouth but it looked too white to be pool filter sand. Any thoughts? I'm more curious then worried at this point, I find it hard to believe that it was an ich parasite that it wouldn't affect the other fish or at least find a different spot on the harlie other then his lip time after time.

My next question is about a betta I recently took in. This guy supposedly rescued the betta six months ago and the betta still looked like crap six months later. After being in heated water for the first time for a few days his fins have already grown back half way and he's super active now. One thing I have noticed on him though are his eyes. They're really cloudy. His eyes also bug out a little but I've had my fair share of bettas with bug eyes so I don't believe it to be popeye. I can see his eyes moving but like I said just super cloudy. Is there a possibility through past trauma he could be partially blind explaining the cloudiness? I wish he wasn't the color he is, he's a plum purple with a metallic sheen over him. Makes him look sick/fuzzy but it's just the coloring. He's a cool fish though, his face reminds me of a mackerel

Thanks for any input.

The guy had a filter in the 2.5gal the betta was in but it's still a very common belief that bettas don't need heat so he didn't put a heater in the tank. I'm not sure how well of a diet he was fed. Despite his last owner having beautiful discus as well as many other fish tanks his two bettas kinda got put to the side. The other betta looks really good but then it again it was provided with a better environment. This betta was kept in the dark, with no heat with one small plastic plant. Both bettas seem happy, both are getting a good diet now. The sickly looking one acts quite macho now, constantly displaying his torn up fins to the healthier one through the plastic canvas. Both bettas are very much appreciating the decor in the tank that they can hide in

The darn harlie has the speck on his lip again, I think I'm going to put him in a 5gal bucket and do a salt treatment on him in the off chance that it is ick(again cant be sure it is ick with its coming and going). I'd be willing to dose the whole tank but are corys sensitive to salt?

For future reference though are corys tolerant of salt?

Thanks everyone, the betta with cloudy eyes hasn't been introduced to any other fish. He's in his own tank. I think my game plan for him is just to keep the water super clean and keep an eye on him. He's already gotten so much more active and started to regrow his fins that I wanna see if good care can remedy the situation. If not I'll take the next step

As for the harlie I'll buy some pimafix and melafix on thursday. So I should do doing on pimafix as instructed and then use melafix. How many days should I use the melafix at half strength?