One dGH is still very low calcium concentration. Why not try adding Equillibrium or other GH booster to get that up around 4 or more? Today I measured my tap water GH again, and it is down to 3 dGH, so I plan to start dosing Equillibrium soon. For the moment my one tank is ok because I have a small rock of Calcium/Magnesium carbonate (I think - it is flowstone) in the tank, and the tank water is around 5 dGH.