whats your tap water pH? its about 7.4 in my area. honestly, i never test my kH etc, but i do test my pH once a week. my 20g tank with 130w pc 10hr/day, co2 with 2 bubbles/sec/24hr. pH is about 6.6~6.8.
my 5.5g tank is weird tho. 48w pc 9hr/day, co2 with 1 bubbles/sec/24hr. pH is 6.0 or even lower. my test kit only can test from 6.0 to 7.8 something like that, but im pretty sure kH is low. water is very soft. hehehe i judge kH by Tonina sp.
it can survive and has new stems come out.
my 2.5g tank just set it up as my connection tank yesterday for short term.
26w pc 8hr/day(haven't turn on lights yet), co2 with 1 bubble/2sec. pH was as 5.5g around 6.0 or lower.
i think pH does matter with how well co2 dissolves in the water.