M Walczak wrote:

I have tap water and my kh is about 16 in a heavily planted tank 29g with
diy co2, gh 12, ph 7.7, NH3 0, NO2 0. How should I go about lowering it
safely? I may know the answer to my own question but I am not a very
confident aquarist quite yet. But how about doing week water changes? Up to
what percentage would be safe to do weekly? My tap water has a kh of about
4. Yes I'm not sure how my KH got so high, my tanks only been set up for 3
months now.

The better question is, how can you keep KH from rising from 4 at the tap to 16
in the tank?

Look for the following:

* Seashells
* Shell fragments in the gravel
* Limestone
* Marble
* Aggregate or cement-type rocks

The aforementioned vinegar test will reveal most of these. Remove the source,
and the problem is solved.