It sounds to me like you may have an ionic imbalance due to low Mg. Seachem has a good article about it here:
aquavitroâ„¢. Calcium, Magnesium and Ionic Imbalance
I am in no way affiliated with Seachem , but I have had many good support experiences with their tech support folks. I use their aquavitro line exclusively to maintain my basic water parameters (pH, alkalinity, calcium, magnesium) with good results. I find the dosing easy and their instructions clear. Also, if I do have any questions, I can tell you from past experience that I will receive excellent support if I need to contact them.
Hope this helps.
/sf