We've go a 70 litre tank. 1 platy, 3 glowlights, 3 clown loaches and 6 neon tetras. Ph has gone to just belowHow many gallons or litres is the tank, how many fish and which type, can you post water stats in ammonia,nitrite, nitrate,and ph.
Laying to one side can be a parasite or bacterial infection, what do you feed the fish, any signs of flicking and rubbing or laboured breathing.
I can see why you ran into problems, see you have glow lighs tetra's, i've still got mine but they fetched gill flukes into my tank, serves me right for not putting them into quarantine.