Seachem Reef Iodine 500 ml.

Reef Iodide™ is a concentrated (8,000 mg/L) stabilized potassium iodide source for reef aquaria that will restore and maintain iodide levels to those found in natural sea water.
It is formulated to provide a safe source of iodide that will not convert to toxic free iodine under storage or reef conditions.
Iodine is as toxic as chlorine and should never be used in a reef system. However, iodide is as safe as chloride.
Iodide is an important element required by invertebrates and many soft corals (gorgonians, sarcophytons, etc).

Directions:
Please note that each cap thread is approximately 1 mL, full cap is 5 mL.
BEGINNER: Add 5 mL (1 capful) for each 200 L (50 gallons*) every other day.
ADVANCED: Add 1 mL for each 80 L (20 gallons*) daily to raise iodide by 0.10 mg/L. If necessary, adjust amount so that iodide reads 0.06–0.08 mg/L 6–12 hours after the last amount. Thereafter, use this amount daily and check iodide twice a month.
EXPERT: After determining the iodide consumption rate, set up a continuous drip system. Use the following formula to determine how much to add to your top-off water: m=0.5vi (m=mL of product to add to top off water, v=volume of tank in gallons*, i=amount to raise iodide in mg/L). For example, if you want to raise iodide by 0.10 mg/L in a 50 gallon* tank, then you would add 0.5x50x0.10=2.5 mL into the top-off water.
HINTS: It is normal for iodide levels to decline after a few days. This results from utilization and chemical depletion. Therefore, frequency of use will vary with different reef tanks. Dosing can be adjusted based on coral response. To check iodide levels use Seachem’s MultiTest: Iodine & Iodide™ test kit.