ph is 6.0 - 6.4
ammonia 0 - 0.25
nitrite 0 - 0.25
nitrate 0
weekly water changes
im sorry Rokuzachi i had typed the wrong numbers for my nitrate they are high +160 and my ammonia it was 1.0 ppm ,my bad
The picture is now clear to me at the moment. The fishes' immune system broke down under such unfavorable water chemistry. Ammonia alone, long-term, will do it. Nitrites are even worse toxins at the same concentration as ammonia. Nitrates are sky-high (granted they cannot be measured reliably but that number is enormous; anything over 20 ppm is not recommended).
I hope you are using a good quality liquid test-tube test kit.
pH is a bit too low but the good thing is that at low pH, the ammonia toxicity is essentially eliminated, you have 1 ppm ammonium NH4+ and not ammonia NH3.
Anyhow, your bio-filter is not coping with NH3 and NO2 (nitrites) and you are not coping with NO3 (nitrates), which are removed by water changes. Everything needs to be stepped up. In a properly run aquarium, both NH3 and NO2 must read zero on a standard liquid test-tube test. NO3 - less than 20 ppm, better less than 10 ppm.
Constant stress --> weakening of the immune system --> bacterial infection and parasitic infestation break-out. I'd say if you right your water and keep it that way, 50%-80% chance they will heal up on their own, without salt or other meds. If you don't, 100% chance they will die.
