Seachem Phosphate Multitest

By Seachem


This kit measures inorganic phosphate to less than 0.05 mg/L, producing a unique easy to read yellow-green-blue color range in marine and freshwater. MultiTest Phosphate performs over 75 tests and contains a reference sample for validation. Range: 0–3.0 mg/L. Precision: 0.001–0.1 mg/L.


1. Fill sample pipette to base of bulb and dispense to a test cavity of the test plate.

2. Add one drop of Phosphate Reagent 1. Add two drops of Phosphate Reagent 2. Stir briefly with stir rod.

3. After about 5 seconds to 30 seconds (or time frame that produces good matching with scale), compare color to chart to determine concentration.

4. Promptly dispose of completed test solutions by rinsing test cavity under running water. If the test plate becomes stained, soak or clean with a dilute bleach cleaner, then rinse well.

Reference test

The proper performance of this kit may be validated by running a test in the normal manner except that the reference sample is used in place of a aquarium sample. It is not necessary to run a reference test to use this kit. The only time you might choose to run a reference test is if you have cause to believe the test is giving incorrect results. If you run a test using the reference sample and obtain the correct result (based on the known reference value provided) then you know the test is giving correct results. To run a reference test, use the Phosphate Reference as the sample in a phosphate test. Reference value is 1.0 mg/L.


Sample volume is critical; you must use exactly one full stem of sample. Low phosphate levels generally develop faster (5-10 seconds) while higher levels take a bit longer (30 seconds). This kit is designed to measure low phosphate concentrations (< 0.05 to 3 mg/L). Very high concentrations will cause a precipitation of the reagent and consequently could be mistaken for a low reading. The appearance of tiny black or blue specks indicates beyond range concentrations. In such cases, prepare a known dilution of your sample with distilled water and test again. Interpretation This kit measures soluble inorganic phosphate, reported as phosphate, not phosphorus. To convert to phosphorus divide result by 3. Natural sea water ranges from less than 0.01 mg/L to 0.3 mg/L. For corals in reef aquaria, such phosphates should be 0.2 mg/L or less. Phosphates are non-toxic to fish and most invertebrates, but are ideally kept below 1 mg/L to minimize algae growth. In freshwater, phosphates are not critical and the allowable concentration is dependent on variables such as nitrate, manganese, iron, and vitamin concentrations, as well as the extent of use of live plants. Usually, freshwater phosphate concentrations will be beyond the range of this kit, and dilutions of the sample with distilled water will be required. If excessive algae growth is not a problem, then the phosphate concentration may be considered as acceptable.