That’s correct, as far as I know I shouldn’t have any Kh which is what these fish wouldn’t like. They’d probably still do ok but there wouldn’t be breeding and colouration may not be as strong on say the nannostomus mortenthaleri for example.i also suspect i have higher gh/kh than you have which would suggest your tds is composed of plant loving nutrients
As I use RO water everything I add is either plant fertiliser or equilibrium. Just so you’re aware I don’t undertake any water testing apart from measuring tds so I have no idea what ph my water sits at currently. As I use co2 I’m guessing it fluctuates a fair amount so I don’t see the bother in trying to work out what it is. I just use tds and the fish to ensure I am keeping conditions to what they prefer.