Low kh, high gh

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AC Members
Mar 10, 2020
Brent, AL, US
Real Name
So, I have this problem off & on.

My kh sometimes gets low, but that's easy to fix with a water change using tap water. And if it's high, which is rare, I can lower it using a mix of RO water & tap. No problem.

But lately, sometimes my kh is low, but gh is really high. So I do small water changes to increase the kh, but am always afraid the gh will go higher, also. So I use a water softener pillow to keep that from happening.

My other parameters are almost always good, including ph.

So here is the question...is there a way to raise kh without raising gh? I can't really find a clear answer for that.


AC Members
Jun 28, 2006
SF Bay area, CA
What is your tap water KH & GH? Is it different at different times of year? Do you have live plants? How many fish in what size tank? What do you consider "good" for all parameters? Do you have rocks (like limestone or real coral) that may add to GH? Fertilizers?

I never worry about "high" KH, my last 2 houses have "soft" water (low GH & KH both). I use a bit of crushed coral for both but if you GH tends to be "high" that might not be the best answer for you.

I have used a little baking soda to raise KH BUT it does add sodium that can build up without large regular water changes. Measuring sodium is a different thing for us freshwater fish people...I think it's potassium carbonate (or bicarbonate?) that raises KH without adding GH or sodium...I'll have to look it up...maybe tomorrow...sorry, close to bedtime.