If your water company report doesn't show any magnesium in the water, either because they just don't list it, or it isn't there, adding some GH booster, or some epsom salts will ensure that you do have sufficient magnesium for the plants needs. I add epsom salts to my CSM+B mix for that reason. But, I almost never open my bottle of Equilibrium GH booster. I think the last time was when I experimented with it a little.