As mentioned do not even bother with that CA
additive unless you have a lot of stoney corals and clams.
Do not ever dose something you have not tested for and if you dose CA
will be affected and so will magnesium.
You are better off with PWC
's if you have a low calcium demand.
As far as the sand, sifting animals help as well as good flow. There is much debate as to what is better, bare bottom, shallow, or deep. The fact is that with proper care all can be kept for a long time.
I know a guy that has had his DSB
for 27 years.