I honestly think sea salt, with it's trace minerals is the best, but chemically salt is salt, as long as is pure with no anti-caking ingredients in it. Canning salt is very fine, easy to disolve and usually a bit cheaper.

So when you are thinking of a salt bath, what are you trying to do? Parasites, or something?

pH somewhere between 7.2 and 7.6, nitrites 0 nitrate 10.. is this acceptable?
Because I thought so.. Ammonia looks to be very slightly at stress level at 0.5 but I did a water change yesterday?

It doesn't matter if you did a water change yesterday, sometimes the parameters can appear without warning.
This is why it's important to test regularly Especially if an aquarium is a new set up.

If ammonia is 0.5ppm you should do another water change, a large water change of around 70-80% should help get the ammonia down.

If you think the fish has parasites, can you actually see them? The only invisible parasites that I know about are flukes, usually you should be able to see something on the fish, to know it's a parasite your dealing with.
Only so far, I've not heard of any parasites being internal?

If you think it's an internal infection, you will need to treat this with medicine. But please be absolutley sure about what illness you are dealing with before treating it. Diagnose Twice and Treat Once.

In some cases when people don't know what the illness is or what's causing it, they start to chuck in medicine, thinking it will help, when actually this can make the problem worse. As medicine can affect the water quality.

You mentioned in another post the fish was being picked on by the others, so could it be possible that his fins are ragged from them bullying?

This website may help (Link is not visible to guests. Please register to view.)
It explains possible illness, with symptoms a fish shows, I hope it helps.

You probably already know this, but;
If the fish seem ill or slightly off Always test the water quality first.
If the water quality is 0ppm for Ammonia and Nitrite and under 40ppm for Nitrate, then you know it's something else.

Usually if I'm un sure on something, I just do a little research
Look for what other symptoms the fish should be displaying with the suspected illness and taking it from there.
It's good that you care so much about them

Sometimes with an illness you are un sure of, it is better to wait and see how things go
For example my goldfish Lucky, one day I noticed veins in her tail and I panicked. I thought she could have a bacterial infection, what if she's haemorhagging somewhere? Someone else mentioned it could be a sign impending fin rot.

The water quality was fine, so I knew it wasn't that and I kept a close eye on her, waiting for something to happen so I'd know what illness I was dealing with. And you know what? Nothing happened.
She wasn't ill. The veins in her tail never got worse, fin rot certainly never showed up and she never had any other symptoms to indicate a bacterial infection, she was perfectly happy and healthy, the veins weren't anything to worry about. I kept an eye on her for 20 days, just to make sure it was nothing serious.
So if she had of been ill, I would have known about it.

So sometimes if you are un sure if the fish is ill, as it seems to be acting healthy, it can be appropriate to wait and see. If the fish is ill, you will certainly find out and if it's nothing to worry about, you'll know that too

Slightly torn fins or stringy poo generally means the fish aren't comfortable, and since your tank is a tad small for all those fish, no wonder All you have to do is keep up the water changes until you'll be able to find a bigger tank

And never use table salt, get some sea salt. It's cheap and readily available in any grocery store