Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Baking soda, @ 1 teaspoon per 30 gallons will raise the carbonate hardness (KH, alkalinity) by 2 German degrees of hardness, about 35ppm. I sure would not use 1 tsp per 5 gallons in one dose. Too high, too-sudden a change.
General hardness of about 70 ppm (ALWAYS include the units when you measure ANYTHING!) is fairly soft, and with your fish choices you probably want to add more minerals for them. GH Booster can do this. The main minerals you are testing with the GH test are calcium and magnesium. Several GH boosters also have potassium, a required plant fertilizer.
If you want to use coral sand, oyster shell grit or limestone based sand, then here is how to get a faster result:
Prepare the water ahead of time, setting up a 5 gallon bucket with a small pump (table top fountain pump is fine, or air bubbler).
Add a generous handful (perhaps 3-5 times as much as is in your filter) of any of those materials, and let the pump run overnight. Add dechlor.
Test the water (GH and KH)
Then do a water change with this water. If the GH and KH are just a bit higher than the tank, then do as large a water change as you want. (100%, if needed)
But if the GH and KH are more than 20% higher than the water in the tank, then do a smaller water change. The goal is to increase the GH and KH no more than 15% in any one water change. You can do this much of a change a couple of times per week. The fish need to adapt to the higher mineral levels.
If the first bucket did not have as high GH and KH as you wanted, then add more of the materials or circulate the water longer.
Now that you have started raising the hardness of the water, keep on doing that every time you do a water change.
By exposing the surface area of fine particles (they have LOTS of surface area) to the moving water overnight you are dissolving the minerals into the water faster than if you were not keeping the water in motion.
Another way to do this is to use any of these materials blended with your substrate, or as 100% of the substrate.
Caution: This can make the water in the tank a LOT harder, and you must match this with every water change, or else the fish will be exposed to the variable levels that happen when you change the water and the new water has too-few minerals in it. Could kill the fish. I would not do this in your situation. (Actually I do this, but for Rift Lake Tanks).
Here is how I do this:
Prep water for water changes by adding:
Add baking soda for KH. carbonates are a buffer that stabilizes the pH.
Add GH booster for GH. (Calcium and magnesium)
Also, my hard water tanks have coral sand or oyster shell grit in the filters or blended with the substrate. The reaction time is slow, however, and when I prep the water for a water change I just add the minerals that would have dissolved out of the coral sand etc.