it might not be high co2 as much as low o2 in the water , try adding some more water movement or add an air pump
O2 shouldn't be a problem as I'm running a wet/dry sump
I don't know about you, but in se Portland I have really soft water
Out of the tap:
Amonos need harder water I add some seachem equilibrium along to my tank and my Amanos do well with co2
Do you have a GH of your tank water you could share?
I have softer water here with a TDS of 17-20... So that's definitely a possibility