I would stay away from such products as Calcium + 3 which contains unknown amounts of Calcium, Strontium, Molybdenum, Iodine. There is no need for Sr, Mo or I. Water changes and food introduced into the tank has enough.
I would also stay away from Purple-Up. It contains powdered aragonite, which can sit on the bottom without going into solution. If the pH drops it will readily dissolve and raise the Alk and Ca++ to very high levels. There have been a number of instances where this has happened.
Turbo Calcium has no effect or pH or Alk it is just CaCl2 in water. Think of it just like table salt, NaCl, only it has Ca++ instead of Na+,
CaCl2 → Ca + Cl2.
Kalk is by far the best additive if it by itself one can maintain their demands of Ca++ and Alk. It is a truly balanced additive and adds nothing other than buffer and Calcium. It is the only additive that does this par a calcium reactor. In water.
Ca(OH)2 → Ca++ + 2 OH
These 2 OH will combine with CO2 and remove it from the tank, no only buffering by adding Alk but raising the pH by removing the CO2. And CO2 is a very big issue in many tanks. CO2 will drop the pH no matter what the Alk is.
2OH + 2CO2 → 2HCO3-
For each 20 ppm increase in Ca++ with kalk there will be a 1 meq / l ( 2.8dKH) increase in Alk.
The addition of kalk or Turbo calcium and how much one needs to raise the Ca++ and what Alk one should have can be seen here using this calculator. So, overdosing is not an issue. There are many additives in this calculator which has a drop down menu. There is also a link for Mg++ addition and tank volumes.
Reef Chemistry Calculator 
Calcium +3 Question 
jb
