Fish dying for no apparent reason

Question
Hi John,

Hope you can help. In the space of 24hrs, i have had 6 of my fish die. there is no disease in the tank (that i can see anyway as the fish look healthy). I have tested the water & all the levels are spot on. Temp is also good.
I have lost 2 tetra's, 2 angels & 1 molly & a glass catfish. My tank spec is:
120ltrs
Fluvel 3 filter
2 air stones
Stock now:
3 small angels, 4 tetras, 1 rainbow fish, 1 moonlight guorami, 1 dwarf guorami, 3 rosy barbs,3 small firemouth cichlids & 1 plec.
i have had no problems for about 5mths & no bullying is going on by the larger fish.
If you need anymore info, please let me know.

Thanks

Rich

Answer
Your tank is very overstocked. The fish are dying because the nutrient levels (also pH probably) are skyrocketing. You have enough fish to stock a 300 gallon aquarium to the max.

You need to get rid of your pleco and alot of your other fish. Then clean the filters and do a COMPLETE (100%) waterchange and gravelvac.

John Kliewer