Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
If the test results were really far apart that might be some pretty odd water, but 4 dKH and 8dGH are not too far apart.
Don't trust the KH/pH/CO2 charts. They are accurate only in water which has only ONE buffer, KH. In an aquarium there are many things that control the pH, each trying to make the pH a little different. That throws off the chart. It can be wildly inaccurate.