Baking soda (Sodium Bicarbonate) is cheaper and readily available. Its also easier to control dosage and effectiveness.
Add 1 teaspoon per 20gallons to raise GH (and KH). premix the solution in a container and make sure it completely dissolves before adding to the tank. Wait 6 hours then retest and repeat as needed. KH will stabilize and help buffer your new PH.
to raise GH, use epsom salt (Magnesium Sulfate).
best to test your GH and KH before attempting all this. a KH of 3 - 5 would be a safe range to maintain a somewhat neutral PH.
Thanks, I wondered how this worked. A friend said she she just puts baking soda in her filter for 125g, but she never told me how much I'm supposed to use per gallon. Whenever I test for GH and KH and it tells you to count...I barely get to 1, the most was 3 and that was a while ago.