It looks like he has more than 1 issue.
In the pictures it looks like you have a bit of finrot that is still progressing.
The last picture, like sakura said looks like ich.
He also seems bloated.
In the first set of pictures it seems that he has some sort of body bacterial infection.
Petco's (at least the one in state college PA) Platys all seem to have ich. If you did not quarantine the platy first there is a chance it could have spread to him.
That being said, Ich doesnt kill the fish it weakens his immune system. Parasites need to have a host to survive, so they will never be the direct cause of death per se.
It's very possible that your betta ether had when you purchased or somehow contracted ich (its pretty common). The ich opened up doors for other infections because of the depressed immune system. Leading to other issues like bacterial infections.
Unfortunately multiple infections are way out of my league. I'm sure sakura or MattsBettas or someone like this can help you out.
Sakura8 - No he does not look like that at all. I'm sorry the pictures are so bad. I do think there is more than one thing, but ich doesn't seem to be one.
Naladari - As for the platy, he didn't have ich either, he died because the fish in my other tank kept picking on him so as a last effort I tried switching him to the tank with Nightwing. He seemed okay at first but then completely withdrew and the next morning he died. He was a good two years old though.
Hello everyone, sorry for the late update, Nightwing does seem to be improving, I have not found any new fuzzy spots, and the fuzzy spots that are there are not as fuzzy anymore. He is more active and eating more also. He seems to be trying to spread his fins a little more, but he doesn't have much to spread. Also, what is CT?
On the down side, my tetra tank now has ich, but I treated it right away and they looked tremendously better overnight!!
Hey that looks like Nightwing before he got sick! Even the color! Jeez these pet stores just put anything on containers huh! Not only is he not a he, but he (she) is not a half moon!!! The Petsmart I went to charged more for him (her) because of the half moon. The label was a male twin tail half moon Betta and they estimated him to be under 6 months old.
By the way, he is looking so much better today!!! His fins look so ragged, but he is sticking up what little fin is there which is good right? Tomorrow he is due for the 30-40% water change. He is eating again, but I am still taking it slow with the food because I don't want to over do it with him. Should I keep the temperature at 76? I usually let it go between 78 and 80 F before he got sick.
Thanks again everyone!!!!!
i guess he's more of a batgirl then... :p it does make sense though, that's a very female shaped body. also female bettas will sometimes get horizontal brown/black "stress stripes" when they're sick or stressed out, which might account for some of the dramatic color change in your pictures.thanks for the update, it's good to hear they're getting better! i would leave the temp at 76 until the fuzz is completely gone though. you don't want it to come back.