Growly Dog wrote:

Has anyone tried to add a hand full of crushed coral to raise and maintain
KH?
I set up a new tank and my hardness is 1 the PH is 6 and I want to add CO2
but fear that the PH will drop.

You will need to raise the KH to 2 or more before you can safely add CO2. The
higher the KH, the less the risk of a radical pH drop.

I keep my KH at 2 with weekly water changes of 30%. If I skip water changes, KH
will drop to about 1.5 after 3 weeks.

If you want more control than crushed coral will give you, use Baking
Soda-Sodium Bicarbonate. It's super cheap, and directly raises KH without
affecting anything else.