Phosphate or Phosphorus Testing with Hanna Checkers?

The Hanna HI736 Ultra Low Range Phosphorus Checker is more accurate at low ranges than the HI713 Low Range Phosphate meter. Many reefers argue that the phosphorus checker is a better option for those reefers who are looking to maintain ultra-low nutrients right at the cusp of 0.00 ppm. Keeping ultra-low phosphate can help increase coral calcification or growth and prevent or fight algae outbreaks. However ultra-low nutrients almost always leads to harder to test for nutrients, and with phosphate that's undoubtedly true. Particularly with test kits because most people find the shades of blue impossible to read confidently, and at the end of the day the human eye is a reasonably poor measurement tool and likely why digital checkers have become so popular.

Before we get too far into this, we think there's one crucial factor to consider, while all of us reefers would absolutely like lab quality accuracy and have our 15 dollar test kits perform like $200 lab grade kits or $50 colorimeters perform like $1500 meters it's just an unrealistic expectation. In many cases because the quality of the components reagents and testing methods are different between the different price points. Also to achieve lab-level accuracy, you need to follow lab quality procedures which include but definitely not limited to;

• Perfectly clean vials
• Cleaned with acid between uses
• 100% of the reagent is used
• Test sampled precisely measured
• Mixing time is accurate to the second
• The mixing is done the same way every time
• Standardized lighting

With Hanna Colorimeters it is imperative the glass cuvettes are crystal clear since the smallest fingerprint or smudge will throw off the results. That said we're not synthesizing pharmaceuticals here, just keeping our reef tanks in that safe, consistent range and most of these tests are designed to get us close enough to achieve that goal without breaking the bank. For home use, it's more important that the results are consistent and affordable than they are accurate to the third decimal, that said if you keep everything clean, measure correctly, and follow the procedure exactly most of the hobby grade test kits including the Hanna Checkers will get you surprisingly close. To see the difference between the two Hanna Checkers, the HI713 Low Range Phosphate Checker has an effective range of between 0 to 2.5 ppm which covers 90% of the reef tanks out there. Where the Hanna HI736 Ultra Low Range Phosphorus Checker measures in parts per billion rather than ppm. The HI736 has a range of 0 to 200 ppb, however, to convert phosphorus to phosphate you will need to multiply the reading by 3.066 and then to translate that to parts per million, divide that number by 1,000.

(5 ppb phosphorus X 3.066) / 1000 = 0.015 ppm phosphate

The net result is the effective range of detecting phosphate is a much smaller window of resolution, 0 ppm to 0.6 ppm phosphate versus the 0 pm to 2.5 ppm of the HI713 Phosphate Checker. Many reefers like the phosphorus checker because an ultra-low nutrient system will likely never be above 0.6ppm. The component of all this at most reefers key in on and stirs a debate is the presumed degree of accuracy of the phosphorus meter, the Hanna Low-Range Phosphate Checker has an accuracy range of ∓ 0.04ppm (+4%) of the reading, meaning if the meter read 0.5ppm phosphate in the tank the accuracy window would be between 0.4 & 0.56ppm. Now using the Ultra-Low Phosphorus Checker let's assume we got a reading of 163ppb which is the phosphorus equivalent of 0.5 ppm phosphate. The accuracy window is ∓ 5 ppb (+5%) of the reading that result is accurate from 0.48 ppm to 0.54 ppm, which indeed is slightly more accurate, but not in a way that has a significant meaning to the average reefer.

So why is the HI736 more accurate?

Simply because the measurable range is so much smaller, the phosphorus checker is only covering a range from 0 ppm to 0.6 parts per million where the phosphate checker range is four times as large. One element to also considers most testing methods are not only less accurate at extreme ends of their testing range. This is also where inaccuracies in procedure and sample or reagent handling are likely to show up as well. Because of that, this is where some of the advantages of the HI736 Phosphorus Checker become apparent; reefers want to measure near zero phosphate levels as accurately as possible. So let's assume a much lower phosphate level in the tank around 0.03 ppm which is the goal for some reefers, but that's also very close to 0 ppm when compared to the overall range. The reading at the extreme end of both meters measuring range, in this case, the accuracy range of ∓ 0.04 (+4%) of the reading would mean the phosphate accuracy window would be somewhere in the range between 0 & 0.07 ppm which is likely a larger window than some reefers might prefer. Particularly if you have 0.03 parts per million phosphates in the water and the meter is reading zero. Now with the ultra-low phosphorus checker a 0.03 ppm phosphate reading would show up as close to 10 ppb phosphorus once we apply the accuracy expectations of the ∓ 5 ppb (+5%) of the reading we end up with an accuracy range of 0.016 ppm to 0.047 ppm this is less than half the range of the phosphate checker. If your measurement goals are tied to achieving these near-zero ranges the HI736 Ultra Low Phosphorus Checker from Hanna is likely a better option as long as you're okay with applying some math to the results you get from the checker.

Reefers who maintain moderate phosphate levels in their system, the HI713 Phosphate Checker is likely going to produce usable results without the math requirement. In most cases keeping your reef tanks readings around 0.02 to 0.03 ppm with the HI713 is perfectly acceptable even with the small margin of error.