Betta looks very unwell.. help??

Hi!
I bought a super delta on sunday, monday night I noticed he was covered in what I can describe as white bits of grit/spots all over his body. I'm new to all this, so researched and found it was ick! I have started treatment, using the api super cure ick, just waiting 48hrs to put another dose in. However, yesturday I noticed he was swimming strangely, and would swim to the middle of the tank and then would just nose dive to the bottom. From late last night and till now he is hiding and wont come out. When I look he is on his side and breathing really fast. I have rang the place were I got him from, they told me to check my ph levels because they have found the water in my area has been quite high lately. So I have just checked. My test results were
Ph between 7 and 7.2
Ammonia none
Nitrite none
Nitrate 5.0ppm
They told me that the fish would of been fine from them and its maybe my water. I dont know what's gone wrong. My tank is now under treatment, I have left my neons in there because I was told the whole tank could be infected now. They are completely fine.

Any suggestions or help would be welcome.
Thanks

Test results sound good.
Can you post a photo of the sick fish and the tank please?

Luckily I have never had ich, but I have noticed most people on here advise to simply turn the temperature up for a fortnight as the pathogen cannot survive heat.

If it's something else though, some people have suggested heat will make it worse (though the human immune system gives us a temperature for a reason)

He is getting worse. This is what he is like now.. and every now and then he moves. He looks even worse. I have noticed the spots have gone today which means now is the time to kill the ick. I have just done another treatment, which is the last one before a water change in another 48hrs. I feel awful and really dont know what else I can do. His fins dont look great could it be fin rot? When I bought his on sunday he looked perfect in his tank, well to keep he did.

What is the history of the tank?

He is literally just balancing now on the wood. Still breathing. He isnt gasping for breath though. Just normal breathing.

Had the tank up and running for nearly two months now. I have 3 neons and 1 harlequin in there. It is a 25L, I bought from pets at home big mistake. They told me I could have the fish I have, 3 neons and 3 harleyquins and 2 mollies. 2 of the harleys died. After researching I knew I needed to get the mollies out my tank because it was too small, so they went into my dads tank and are fine. And my fish since then have all been fine.. so I decided to get a betta and now this has happened.

It's possible the medication you are using is making him feel sick. Some medications create an oily film at the surface that is bad for labyrinth fish. I know the water quality results were good, but I'd be tempted to test again just to double check they haven't got worse. The pH and gH may well be inappropriate long term but I doubt they are causing this particular issue.

Do you think swim bladder disease maybe? I'm at a loss because I really dont know what it could be. Unless he was sick when I bought him. But the shop told me it wouldnt of been because they are kept in individual tanks. If I'm honest I'm new to all this so when picking him I wouldn't of known what i should of been looking for. I will test my water again now and see if it has changed

When I first tried fishkeeping in my teens before I even knew what the internet was, I killed several fish in weeks. They all appeared to have what the books in the library described as swim bladder disease.

Here's the thing though - that disease is said to be extremely rare. I am now convinced I killed those fish with either ammonia or nitrite or possibly chlorine (or all the above).

Just checked my water and the results are the same still

I dont think he will make it through the night. He is now on his back just lying there. Still breathing.
Because I am new to this and feel awful if i killed my fish, I test my water all the time and do weekly water changes. If I'm honest maybe my tank is just not old enough maybe. Maybe I should have waited another month

It seems a bit. weird, yeah. Especially if your neons are fine despite being in too small a tank and in too few numbers, I would expect a Betta to be hardier than them if anything.

Unless the medication doing doing more harm than good.

A Betta being bullied to death by three neons seems far fetched - but possible I guess, they have tiny piranha like teeth I believe

My neons and harley are doing amazing, I felt nasty on my harley being on it's own at first but it hangs round with the neons and is absolutely fine. My betta never bothered with the neons and they never bothered with him. When he first went in he chased them for like 2 secs and then just kept his distance l. But to be honest I got him on sunday and by monday night he started being unwell so i dont think he has even had a chance to do anything. It's awful! That's why I feel like something might have been up with him before I bought him.