There are many different barnds of 2 part calcium additives on the market lucky, you might try a different brand if its availiable in the area i've gotten hung up on the kent tech cb and dont want to change unless i see there is maybe better.
Two Little Fishies C-Balance, ESV B-Ionic Calcium Buffer, AquaC CompletemBalanced Calcium & Alkalinity Supplement, Kent tech cb, Kent Nano Reef Part A & B.
just to name a few. the last one is made for the smaller systems.
Calcium (Ca)This is a measure of the total amount of calcium held in our water in ppm.
Ideally this should be around 380-450ppm. Corals, coralline algae, and clams can use a massive amount of Calcium, especially in heavily stocked tanks so its important to keep levels up via the use of either a Kalkwasser 'calcium Hydroxide' (lime-water) drip over night, to help maintain balanced Ph/Alkalinity/Ca.
Or a preferred method, a proper Calcium reactor in the case of high demands, or a 'balanced' two part additive in the case of low demand aquariums, not to mention regular water changes.
Calcium may be boosted separately of other parameters when required (i.e. if you are out of balance) by the careful use of Kent's Turbo Calcium or Calcium Chloride via a drip.
(A low test kit reading may also be linked to low salinity)
Corals struggle to utilize Ca if levels are below 360ppm, whereas precipitation will occur if levels are pushed much beyond 590ppm. Always maintain NSW levels of 425ppm where possible, and in balance with Alkalinity.
source: Andy Hipkiss basic chemistry
I have had success with the 2 part additives i use Kent tech cb. its a 2 part calcium and alk buffer system equal parts of each are added daily
