Chemistry is a mess. Please help.

[LeanneP]

I was only dosing alk but then I realized I was out of balance because my alk was actually dropping the more I dosed and my Ca started dropping too. I dosed only Ca yesterday for awhile but then my alk dropped again too. I have got my Ca to 420 but then it is still dropping so I have continued increasing how much I am putting in. Alk was up to 6.4 from 6.1 but now my alk is down to 5.4. I am dosing too much alk? I have read and read and I have been doing water changes but nothing seems to be working.
When I called j & l I was told my system would be about 63 gallons so that is where I was getting my numbers from in doing a 20 gallon water change. I have my mag high because I was told earlier that it was good to have mag high if alk was low.
My test kits are all new so I now they are accurate. I am almost getting to the point of just selling everything because I am so frustrated. I am amazed that I haven't really lost anything, but my long tentacle anenome has not been happy. He has let go of his foot hold 3 times since this has been happening.