Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Nate, Sounds like most of the GH in your water is from calcium, which can lead to magnesium deficiency. Also, the GH is not a stable quantity, is always rather low, and sometimes very low, leading to deficiencies in both Ca and Mg.
I would dose GH booster in the tank or at least with each water change, to get the GH to a stable 3 degrees. If you know that the calcium is always there in the water, then you can try Epsom salt (doses magnesium, but no calcium) or perhaps just enough GH booster (which doses both Ca and Mg) to keep the GH at 3 degrees, then just a pinch of Epsom salt to balance the Ca in the water. As a general guide, most aquarium plants seem to do well when the Ca:Mg ratio is pretty close to 4:1. That is, 4 parts calcium to 1 part magnesium. This does not have to be exact, though, and the GH booster plus the small amount of Ca in the tap water without adding Epsom salt might be about right.
If you are keeping hard water plants you might want to dose enough GH booster to raise the GH closer to 5 degrees.