FishMan wrote,
I have been adding ph Stable to
the water to increase the KH, but it seems to be stuck at 0.

You can raise kH by adding sodium bicarbonate (baking soda) - to keep
it there, add a garden size marble chip or two, to your filter. Marble
won't dissolve near as fast as crushed coral...
Instead of using RO water, a drop or two of hydrochloric (muriatic)
acid placed in a 5 gal. plastic bucket of water and let to stabilize
for 24 hours will drop the pH to 5.4. You can then bring pH back up to
what you want with the baking soda................ Frank