You do not need to have a high KH for things to work with CO2. pH and KH are just datas used to find CO2 level in water. You can have a KH of 1 and things would still work and you need not expose your fish/critters to constant changing of salt level content by bumping the KH up every water change which can stress them. I just use my tap water and then add the CO2 and nutrients.
Regards
Peter Gwee
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