• Genuine Red Sea part R21431 — the same reagents and reference standard Red Sea supplies in the complete Iodine Pro kit.
• 50 tests restored — the full test count of the Iodine Pro test, without rebuying the glassware.
• 0.01 ppm resolution against a 0.06 ppm target — fine enough to show a dose landing, where a broad colour kit reads the same before and after.
• Includes the 0.06 ppm reference standard — Red Sea's safety data sheet lists Reagent A, Reagent B and the Standard 0.06 under this refill's part code.
• No timer needed — the reaction is complete when the standard vial matches the colour chart, so the method self-times.

It is the reagent refill for Red Sea's Iodine Pro test, kit part R21430. We do not currently stock that standalone kit.

The same 50-test Iodine Pro module also sits inside the Red Sea Coral Colours Pro Test Kit alongside the potassium and iron tests, and this refill is the iodine restock for it. Red Sea also publishes a combined Trace-Colors Pro multi test refill covering all three elements, so if you own the multi kit, check the reagent bottle labels against R21431 before ordering — you may want the combined refill instead.

It does not fit any non-Red Sea iodine test, and it will not refill a potassium or iron test.

• Red Sea Iodine Pro reagents and the 0.06 ppm reference standard, enough for 50 tests

Reagents only. The 10 mL syringe, glass vials, colour reference card, instruction manual and storage case come with the complete kit. So does the supplement — Trace Colours A (Iodine+) is a separate purchase.

Below 0.06 ppm

Dose Trace Colours A (Iodine+), which supplies iodine along with the other halogens, bromine and fluorine. Red Sea's guidance is to test the colour elements weekly while dosing daily.

Above 0.06 ppm

Red Sea's instruction is direct: change 50% of the water and halve the supplement dose. Iodine becomes toxic above natural seawater concentrations, and the warning signs are soft tissue regression in hard corals and pale colouration in soft corals.

Reading zero on a tank you are dosing

Confirm the reagent is in date before you increase the dose. At a 0.06 ppm target, an aged reagent and an empty tank look identical on the colour card.

Rinse the glass vials in RO water between tests. Residual reagent biases a colorimetric result more than most people expect at this concentration.

Store the reagents closed in their original containers, cool, dry and away from direct sun and large temperature changes. Keep them away from acids, alkalis, oxidising compounds and metals.

Do not tip used test water back into the aquarium. Red Sea classifies Reagent A as toxic to aquatic life, so spent samples go down the sink, not into the sump.

Red Sea's safety data sheet covers this refill and the complete kit together. Reagent B carries the signal word Danger — it may be corrosive to metals and causes severe skin burns and eye damage, and is listed as containing nitric acid 70% at 25–50% and ammonium iron bis(sulphate) at 5–10%. Reagent A is classified as toxic to aquatic life and contains sodium nitrite at 4%. The reference standard contains potassium iodate at 5–10%. Reagent A and the standard carry no signal word.

Keep out of reach of children. In the eyes, rinse with plenty of water for at least 15 minutes and get medical attention. If swallowed, do not induce vomiting — if the person is conscious, wash the mouth thoroughly with plenty of water, and seek immediate medical attention.

Suitable for: reef aquariums running Red Sea's coral coloration programme, anyone already dosing an iodine supplement without measuring it, and anyone whose Iodine Pro reagents have run down or passed their date.

Not suitable for: a first purchase, since there is no glassware or syringe in this box. It is also not for freshwater or planted tanks, and it is not the right first test on a system whose calcium, alkalinity and magnesium are still moving — foundation comes before colour.

• Red Sea Coral Colours Pro Test Kit — iodine, potassium and iron in one case, and the kit this refill most often restocks.
• Red Sea Trace Colours A (Iodine+) — the supplement you dose against the reading.
• Red Sea Trace Colours ABCD Trial Pack — all four colour supplements in 100 mL bottles.
• Red Sea Potassium Pro Reagent Refill — the next reagent in the same case to run out.
• Red Sea Reef Foundation Pro Multi Test Kit — the calcium, alkalinity and magnesium testing this programme assumes is already stable.
• Red Sea range — the rest of the Reef Care testing and supplement program.

Reagents are consumables and carry no service warranty. Any manufacturer warranty Red Sea offers applies in addition to your rights under the Australian Consumer Law, which are not limited or excluded by it. A pack arriving leaking, damaged or out of date is replaced.

Ships as a standard small parcel. The reagent volumes are well under the threshold for dangerous goods handling, so no special freight applies.

How many tests does the Red Sea Iodine Pro reagent refill provide?

The refill provides 50 tests, which is the full test count Red Sea specifies for the Iodine Pro test.

What does the Red Sea Iodine Pro test actually measure?

It measures total iodine, counting both iodide and iodate, over a range of 0 to 0.09 ppm with a resolution of 0.01 ppm. Red Sea's published reef target is 0.06 ppm, which is the concentration found in natural seawater.

What is the part number, and does it fit the Coral Colours Pro kit?

The refill is Red Sea part R21431 and the standalone kit is R21430. The same Iodine Pro module sits inside the Coral Colours Pro multi test kit, so this refill restocks its iodine test — though Red Sea also sells a combined multi-test refill covering iodine, potassium and iron together.

My iodine reads high. What should I do?

Red Sea's instruction is to change 50% of the water and reduce the supplement dose by half. Iodine is toxic above natural seawater concentrations, and an overdose shows as soft tissue regression in hard corals and loss of colour in soft corals.

Can I pour the test sample back into the tank?

No. Red Sea classifies Reagent A as toxic to aquatic life, so used test water and reagent should be disposed of down the drain rather than returned to the aquarium or the sump.

How often should I test iodine?

Red Sea's guidance for the colour elements is to test weekly while dosing the supplements daily. Weekly testing catches a trend before a level runs away, without burning through 50 tests in a season.