My Fish All Stay At The Back Of The Tank

I have a 20 gallon tank with 2 ballon mollys, 1 guppy, 1 platy, 3 neon tetras, 3 nerite snails and 3 albino corys.
Recently all my fish except for the neons and corys have been hanging out at the top and back of the tank they don't seem to be gasping for air and will sometimes swim around but then return to the back they are also all eating well.
My tank perimeters:
Nitrites:0
Nitrates:5~10
Amonia:0
Is it normal or is there something wrong with them?

 

That is never a good sign. Do they have white stringy poop? When mine started staring at the corner, there was white stringy poop which was a sign of either bacterial infection or parasites. I used General Cure which worked wonders. It covers both bacterial infections (metrodizanole) and parasites (praziquantel).

Is it a 20L (30" long) or 20H tank? What temperature do you keep the tank? What is your filtration? How often and what percentage do you do water changes?

You have some stocking and temp incompatibilities. Neons (cooler temp) and cories (warmer temp) should be in schools of 6 or larger. Mollies have a pretty big bioload and I wonder if a 20 gallon is big enough for them without even considering the rest of the stock. I am definitely not a stocking expert, but you should look into that as the bioload is probably too high. Maybe some others that are better than me at stocking will chime in with advice.

 

I did notice the platy having white stringy poo but he was the only one.
It's a 20 gallon long and I'm not sure what the filter is as it came build inside the aquarium it kinda lookes like a tupperware if that makes any sense it has biomedia and those white cotton sheets(don't know the name) inside, I keep the tank temperature 28ºC (82 farenheight I think), as for water changes I do about 25%~30% percentage everyweek or if I see the tank is too dirty.
As for the stocking I started keeping fish early this year and made the mistake of going with what the lady's at the story recomended I had more fish but gave them away and ended up with this combination of fish I also had some problems with ick that ended up killing 4 of the neon I had (that's why there are only 3).
I haven't really seen any major issues with the tank and it's stocking other than they going to the back.

Oh and the fish do swim around some times mostly when there's no one watching, one of the ballon mollys does sometimes try and nip at the others but that's mostly when I give food I feel like she's the boss of the tank, and I do have plans to if possible move them to a bigger tank.

 

The tank temp is definitely too high. Slowly lower it 1° every hour until you reach 74°F/23°C

Keep monitoring all the fish' poo to see if you notice any more white poop.

I'd also up your water change schedule to 30-40% weekly.

Do you still see any ich?

Also, a nice trick I do for my neons is I tape a mirror to the outside of the tank. Any schooling fish will school with it's reflection until you can reestablish the school.

 

The ich was cured none of the fish have any signs of it as for the temp I believe I put it higher when I was treating the tank for ich and for some stupid reason forgot.
Thank you for your replys I will lower the temp and keep a closer eye on them