Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
1 teaspoon of baking soda added to a 29 gallon tank raises the KH by 2 German degrees of hardness. I dump the baking soda into the HOB filter to dissolve. Or sprinkle it directly into the tank right in front of the filter outlet. Dissolves almost instantly. Or I just dose my hard water tanks when I do a water change (adding it to the new water). Through the week they maintain the right KH because of the coral sand substrate.
However, if you want to make a liquid solution:
Figure out how much baking soda you want to add over the course of... lets say a week.
Decide how often you will add it. (lets say you will divide the weekly dose so you add something twice a week)
Dissolve the weeks worth of baking soda in whatever amount of water it takes. Add half of that on Monday and half of that on Thursday. You will have to shake it up well on Thursday, it settles when it is concentrated.
If you want to add just a little bit every day, then I would make some sort of volume that can be divided by 8. For example, 1 cup. Add 1/8 cup daily, every morning, and use the rest when you do a water change.
Alternatives to baking soda:
Add some of these to the filter, in a nylon stocking:
Coral sand, Oyster shell grit (sold for caged birds), limestone based sand or fine gravel.
Use some limestone based rocks in the decor.
Seashells and coral will work, too, but are not really appropriate in a fresh water setting. OK, I suppose, if you have the bubbling scuba diver or ceramic merperson.