Testing your Reef Tank’s Phosphate
Our primary orthophosphate testing instruments for the hobbyist reef market are the HI713 Low Range (LR) Phosphate Checker HC and the HI736 Marine Ultra Low Range (ULR) Phosphorus Checker. The HI736 is labeled “marine” because it is specifically designed for saltwater and utilizes an absorbance curve for marine environments, while the HI713 can be used in either freshwater or saltwater. The HI736 ULR Phosphorus Checker has a range of 0 to 200 ppb PO₄-P orthophosphate as phosphorus, which correlates to 0.003ppm to 0.613ppm PO₄3ˉ. The HI713 LR Phosphate Checker has a range of 0.00 to 2.50 ppm PO₄3ˉ orthophosphate. Both Checkers use an adaptation of the Ascorbic Acid method, with an LED light source at a wavelength of 525 nm and a silicon photocell as a light detector.
Which Checker is Right for You?
The HI713 LR Phosphate Checker is a better fit for reef tanks housing coral species less sensitive to phosphate, such as certain soft corals. The HI713 LR Phosphate Checker is also ideal for aquarists who have freshwater aquariums or fish only saltwater tanks (FOWLR). The HI736 ULR Phosphorus Checker is designed for reef tank owners keeping SPS corals and aquariums aiming for low phosphate levels less than 0.03ppm. While the HI713 LR Phosphate Checker will work for any saltwater aquarium, the unit has an accuracy statement of ±0.04 ppm ±4% of reading. This means if your HI713 LR Phosphate Checker displays a result of 0.08ppm, the measurement uncertainty is from 0.04ppm to 0.12ppm, which can be problematic for certain reef aquarists. Displaying the results in part per billion phosphorus gives a narrower range for detection, but increased accuracy at low range phosphate concentrations desired by many reef tank hobbyists.
The HI736 Marine ULR Phosphorus Checker should not be confused with a total phosphorus test. Testing for orthophosphates is standard practice for saltwater aquariums and provides valuable insight into your reef tank’s water chemistry to help ensure long-term coral health.
