CO2 to keep pH down at higher kh

[flaggy]

g'day

at the moment, my pH is around 6.5 which is roughly where i want it. however, the kH is dangerously low. whenever i try to raise the kh, the pH goes up with it (no real surprise there).

i am also resisting using phosphate-based buffers.

i'm thinking of adding CO2 to my fish-only, 200-litre tank in order to maintain the pH at where it is but with kH much higher, say 4-5 dH.

Bearing in mind this is a fish-only tank (with silk plants), what would be the cheapest "minimalistic" setup to add CO2.

thanks!

[DR.V]

why do you want high kH ?

where are you from ? can you edit your profile please...

Sydney water is fine ...

[sharkbaitnemo]

Keep in mind that CO2 will maintain pH by lowering your pH but won't increase it if it falls too low. Combining CO2 with the low kH will cause a drastic pH crash and a CO2 unit will not help bring the pH back up.
Sounds like you must be using rain water or RO water to have such a low kH value.

[anti-generic]

too much CO2 will suffacate your fish.
theres no point for co2 for a plantless tank.