Found this on 3reef.com and thought I'd share for future references

SALTWATER CALCIUM TEST INSTRUCTIONS

Why test for Calcium?
Monitoring calcium levels is essential for keeping a successful reef aquarium. Reef organisms use calcium to build a calcium carbonate skeleton. Over time, as the calcium in the water is utilized, the calcium level will gradually drop. Calcium must be present for corals to grow. Even reef invertebrates such as crustaceans, mollusks and encrusting algae, require calcium to grow and remain healthy.

Calcium levels drop as it is used by invertebrates or as it reacts with excess phosphate. Making a partial water change may help to maintain proper calcium levels, depending on the brand of salt mix. Special calcuim additives are also available. Elevated phosphate precipitates calcium, rendering it unavailable to reef organisms. Phosphate enters the aquarium from tap water and as a byproduct of fish and invertebrate metabolism. Use Aquarium Pharmaceuticals Phosphate Test Kit to test for phosphate. If necessary, use Aquarium Pharmaceuticals Phos-Zorb™ to remove excess phosphate. Phos-Zorb is a special phosphate-removing filtration media that comes in a flow-through pouch. It conveniently fits into any filter.

Carbonate hardness (KH), often referred to as alkalinity, is important for reef organisms. As carbonate levels drop the pH becomes unstable. The carbonate hardness level (KH) should be 7-10 dKH [125 – 179 mg/L (ppm)] to encourage growth in a reef aquarium and maintain pH. Use the Aquarium Pharmaceuticals KH Test Kit to measure the carbonate hardness. Add Proper pH 8.2 to increase carbonate hardness and stabilize the pH to 8.2.

Testing Tips
The Calcium Test Kit reads the calcium concentration in milligrams per liter (mg/L) which is equivalent to parts per million (ppm).

Directions
Read thoroughly before testing. Do not allow test solutions to get into aquarium.
To remove childproof safety cap: With one hand, push red tab left with thumb while unscrewing cap with free hand.

1. Rinse a clean test tube with the water being tested.

2. Fill the test tube to the line with the water being tested.

3. Holding the bottle vertically, add 10 drops of Calcium Test Solution #1 to the test tube, cap and shake for 10 seconds.

4. Shake Calcium Test Solution #2 bottle vigorously for 10 seconds.

5. Holding the bottle vertically, add Calcium Test Solution #2, drop by drop to the test tube until the solution changes from pink to the blue end-point. Each drop is equivalent to 20 mg/L (ppm) calcium (Ca2+). Cap and shake the test tube between drops. Be sure to count the drops added.
a. A pink color should form after the first drop.
b. If a blue color forms after the first drop, the calcium concentration is 20 mg/L (ppm) or below.

6. As the end-point is approached, the color will usually change from pink to purple before finally changing to blue. After the purple color forms, only one or two more drops should be required to reach the blue endpoint.






# of Drops mg/L (ppm) # of Drops mg/L (ppm)
Calcium(Ca2+) Calcium (Ca2+)
1 20 14 280
2 40 15 300
3 60 16 320
4 80 17 340
5 100 18 360
6 120 19 380
7 140 20 400
8 160 21 420
9 180 22 440
10 200 23 460
11 220 24 480
12 240 25 500
13 260 26 520

Note: Reef aquariums should have a calcium (Ca2+) concentration of between 400 to 500 mg/L (ppm). To save time, rather than adding only one drop at at time, several drops of Calcium Test Solution #2 may be added simultaneously at first, then the final drops can be added drop by drop as the endpoint is approached.
For example, if you think that the saltwater being tested contains about 400 mg/L (ppm) calcium, you can add 10 to 15 drops of Calcium Test Solution #2 at once as indicated in step 5, then cap and shake. If the solution is pink, continue adding drops, one at a time, until the end point is reached. If the solution is blue, then too many drops were added and the test must be repeated, adding fewer drops initially or adding the drops one at a time.