Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
My tap water KH is around 4-5 degrees most of the time, rarely drops to 3 degrees.
I have used several similar products. Soil Master Select and Turface also remove the carbonates.
Basic method, done this summer cycling a 88 gallon tank with one bag (40 lbs) STS:
Test KH. This is when I saw the tap water had dropped to 3 degrees. Odd. It has been 4-5 degrees for years.
Test the next day: KH is 2.
Add 1 teaspoon baking soda per 30 gallons, to raise the KH by 2 degrees so I added 3 teaspoons. (Easy math: pretend the tank is 90 gallons. It pretty much is, because I have 2 canisters running on it)
Let it circulate a couple of hours and test. KH is now 4 degrees.
And so on...
I added more, then less, a lot more, waited longer... One of the things I am checking is to see that the recipe is the same for different amounts of change in KH. It is.
Here is the basic recipe:
1 teaspoon of baking soda added to a 29 gallon tank will raise the KH by 2 German degrees of hardness. Again, the shortcut of calling it 30 gallons is just fine. This is not rocket science. It is a lot closer than hitting the side of a barn, though.
You can use this formula for any tank size, any dose, any change of KH.
40 pounds of STS can remove at least 1 degree of hardness per day from about 90 gallons of water, though I was not really keeping that close track of it.
Once the tank was cycled I quit adding baking soda.
In my other tanks, SMS for example, it kept removing the carbonate for a couple of years. I was only dosing small amounts of baking soda, but I was keeping up with weekly water changes between 25% -50%.
In another tank I mixed coral sand + turface, about 50/50.
In this tank the KH never dropped.
I was running it for Lake Tangayikan Shell Dwellers, so water prep meant adding baking soda and GH booster so it would start off hard, not cause a drop in the water parameters for the fish. I never had to add baking soda mid week. The coral sand satisfied the Turface ability to remove carbonate.
It is still that way today. I moved the tank, then set it up with the same blended substrate. Even without adding baking soda the KH is higher than other tanks. I think the Turface is saturated and the coral sand is now giving its minerals to the water.
Here is how I would do this:
A) Soft water fish. Do nothing. Let the substrate remove the KH. The pH will drop. This can be a problem when you are cycling, and need the bacteria to grow as fast as possible. So add enough carbonates or bicarbonates to get it cycled.
B) Hard water fish. Add things to the tank like limestone sand under the substrate, holey rock, or other coral/limestone/oyster shell sort of material to the filter to help make the water hard. Monitor it and do not allow it to drop. Since this might mean adding a lot of sodium from the baking soda, you might look into potassium bicarbonate or other source of carbonate.
C) In between sorts of fish. If they do not mind that soft water, then let it go. If they really need it harder, then do some of the options in B), but it might be more of a tightrope to maintain the water just right, not too hard, not too soft. Definitely need a KH test. Once you get it figured out, though, it might be as easy as adding a little potassium bicarbonate with every dose of fertilizer. Not much, but some.