Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
KH is carbonates. These are a buffer that can stabilize the pH. When they are so low the pH can be controlled by other things. To raise the pH you really want to start by raising the KH.
Baking soda or potassium bicarbonate are 2 materials that can raise the KH very quickly. Good when you are doing a water change to make the new water match the tank, and will work even with fish in the tank when you are very careful not to add too much at one time.
Adding a material in a bag to the filter is a slower way of doing this, and most of these materials will also raise the GH. Coral sand, limestone that has been ground to the consistency of sand, oyster shell grit (Sold for caged birds) are good materials for this. Larger rocks of limestone and its related materials or shells in the tank can slowly dissolve and can raise both KH and GH.
I would test whatever of these you might already have on hand. Put a cup of water aside with a tablespoon of coral sand etc. in it and monitor the GH, KH and pH for several days. If you have any limestone rocks, or sea shells you could try them, too. They are slower, so set up the glass of water where it won't be disturbed for several days, then test about once a week for a couple of weeks. Top off the glass as needed.
When I tried this with a ground rock called Dolomite it changed within a couple of hours.
Add to the tank some baking soda starting with this recipe:
1 teaspoon of baking soda added to a 29 gallon tank will raise the KH by 2 German degrees of hardness. This is enough change for one day, let the fish get used to it, then add more the next day.
Organic materials like wood, peat moss add organic acids to the water, which lowers the pH. Some of them can also act like an ion exchange water softener, removing Ca and Mg. If they are doing this you would see the GH going down. Equilibrium adds Ca, Mg and K (Potassium). So, if the wood is making the GH go too low for the fish you want, then Equilibrium is a good thing to add. It won't do anything about the KH or pH, though.
When you have several things in the tank that can alter the pH the charts that relate CO2 to pH and KH are not accurate. In this case, the cypress wood is the other major thing altering the pH.
Here is how I handle my hard water tanks:
1) Set them up with some slow release material like coral sand so there is a constant slow adjustment that raises the GH and KH, and the pH will rise as the KH rises. Some have coral sand substrate. Others have oyster shell grit in a nylon stocking in the filter.
2) When I do water changes adjust the new water with baking soda or potassium bicarbonate for KH and Equilibrium for GH to what I want the tank to be.
3) Monitor the tank through the week to get to know if it needs further adjustment. Usually it does not, unless there is something removing the minerals or carbonates faster than they are dissolving.