Fair enough, It was not meant as an attack but RO cannot sustain life, and I do agree that a stable pH is more important than people give credit for.
Reverse Osmosis water must be cut with, in the case of freshwater, either a buffering agent such as Kent RO rite or with a percentage of treated tap water or in the case of marines, used with the synthetic salt when initially adding the water.
Neat RO can be added to a marine tank when topping up the levels due to evaporation
Steve
i don't understand why RO water would kill most of your fish, have you added anything else to it?
It is not what you have added to the water, it is what you have taken away
When you have removed the water for water change, you have taken away water with buffering potential and added water with no buffering potential whatsoever, so ( and this is hypothetical ) it has been a while since the last water change and the buffering capacity is close to exhaustion, you have now decreased it even further, so this allows a pH crash to happen.
have seen it often and when it happens it happens quite quickly.
Steve