Need help with math

[Randy Holmes-Farley Verified Community Expert]

To make it a bit heavier. What woud it be if I slowly add 20% kH 9 water to my tanks of 1000 gallons and kH 8 and just let the panik owerflow lead the water to the drain.
I know if I empty 20% and then refill kH will go to 8.2 but the corals at the top will die. So a continous water change is the only way to go.

If you are sumpless and do not want to expose corals during a change (some seem to be fine exposed, and are in real coral reefs) then many small or a continuous change is a fine plan. I did that (something like 20 x 15 minutes of changes each day), but for other reasons.