Unknown disease

[loaching]

i have a 2 foot tank with 4 gourami's, 9 tetras, 5 widow tetras, 9 white clouds, 1 platy, 1 swordtail, 2 mollies, 2 guppies, 2 small barbs, 2 peppered catfish.
the other day i bought 2 platies and a swordtail. after they had been in the tank for about a day one of them died. before hand it was swimming close to the top of the water and staying still. the next day after the platy died one of my neons died.
Just recently i witnessed one of my guppies staying still near the surface and then seemed to lose its sense of direction cause it was swimming in all different directions. it then died.
some of my fish have been irritated by something and seem to try and scratch themselves on things or have a spas.
temp:27C
Ph:7.2
undergravel filter

Any info on what disease this might be

 

[Vip]

Undergravel filter do NOT do anything at all, they just hold all thr crap under the gravel were as you need to get it out of the tank, i say its amonia killing your fish because your tank is very overstocked.
Do a 20% water change and get yourself a real filter and a vacume for the tank (Clear Tube lfs will have it) chuck out that undergravel there pointless.