Too high KH & PH?


Lifetime Charter Member
Lifetime Member
Mar 8, 2005
Sebbersund, Denmark
a friend of mine has quite hard water. a PH of 8.5+ and KH of 18, GH is 11.

He says he has to lower PH&KH with acid to lower it to a point where his fish and plants can thrive.

He has a Calcium layer on his anubias, and says his plants turn red & die when he doesn't premix the water with acid.

What gives?

He says that everything is fine when he does mix the water.

Can this really be?

He want to have low maintenance tank with CO2 and no waterchanges..
This would be quite hard with his tapwater?

Any suggestions?


Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Sacramento, CA
Re: Too high KH & PH?

The two ways to lower pH are:
add CO2
add RO water

The way to lower KH is:
add RO water

Unless you are trying to grow some of the very few plants that really do seem to only grow in soft water, why bother doing anything to the KH or pH?


Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Re: Too high KH & PH?

There is a relationship between pH and the amount of CO2 that water can contain. At very high pH levels (above 8) the disssolved CO2 approaches nil, to use a soccer/football term. A very few plants can live in such an environment.

With such a high KH I would think it would take a lot of injected CO2 to lower the pH materially.

Reducing the KH via RO is one approach to solving the problem. Another is to find a source of "wild" water that is softer and can be used to cut the hard water.

Good luck!