My fish were very active and eating very well, since about 2 days ago
they are hiding and not eating well and some, not at all.
These are angelfish, neon corys, 11 otos, 12 cardinal tetras.
Six (6) cardinal tetras have died in the las 3 days and think they are the ones with very drawn(empty) stomachs.
125 gal/100 gal net started 9/17, planted tank 10/11.

The significant change that I notice is PH now 6.4 from 6.6.
Have been dosing the same for 6 weeks except for a small increase in Plantex
and new dosing of Epson salt , 3.0g, 2x week.
Temp is about 80-82 F and steady.
There is green algae. Today I changed 50% water and they came alive for a while in the fresh water but reverted to the above behavior.

Any ideas?

tks