Seachem Reef Strontium 500 ml.

Reef Strontium™ is intended to restore and maintain strontium to levels found in natural seawater without affecting pH.
Strontium is utilized in the same manner as calcium and holds a similar importance in maintaining a vigorous level of growth.
Reef Strontium™ contains 10,000 mg/L of available strontium as a gluconate complex. Gluconate complexation confers several benefits: it increases the bioavailability of the strontium, it provides a rich source of metabolic energy to help maintain peak coral growth, and it inhibits strontium precipitation/alkalinity depletion.
Gluconate contains no nitrogen or phosphorous, thus it is biologically impossible for it to lead to algae growth in a properly maintained reef system.

Directions:
BEGINNER: Use 1 capful (5 mL) per 80 L (20 gallons) twice a week.
ADVANCED: Check strontium level, then follow dosing regimen above until strontium is adjusted to 8–12 mg/L. Each dose will raise strontium by about 0.6 mg/L. Size or frequency of dose can be adjusted. Thereafter, use as required to maintain strontium.
EXPERT: After determining the strontium consumption rate, set up a continuous drip system. Use the following formula to determine how much to add to your top-off water: m=0.4vs (m=mL of product to add to top off water, v=volume of tank in gallons, s=amount to raise strontium in mg/L). For example, if you want to raise strontium by 2 mg/L in a 50 gallon tank, then you would add 0.4x50x2=40 mL into the top-off water.
HINTS: Use the Reef Status™: Strontium test kit to measure strontium.