This is part of a series on Aquaponic Water Testing.
Phosphates are one of the three main nutrients for plants. Phosphorus deficiency symptoms are not very distinct. The most common symptom is dwarfed/stunted plants. Tomato, lettuce, and brassicas can develop a distinct purpling of the stems and underside of leaves. Leaves may develop a blue/gray luster under severe deficiency conditions. A brown netted veining can occur in older leaves under severe deficiency.
Test for Phosphate in Aquaponics
All tests measure only “Total Reactive Phosphates”, which is roughly equal to Orthophosphates.
Plants can only take up Orthophosphates
Total Phosphates can only be measured with a high temperature chemical digestion.
Total Phosphate – Orthophosphate = “Organic Phosphate Bank”
Tests can provide results in Phosphorus (P) or Phosphate (PO4).
P = PO4 / 3.07
Most of these test methods will suffer from Fe-EDDHA interference. The API kit, and Hach Method 8048TNT have proven free of Fe-EDDHA interference in my testing. Look forward to an upcoming post regarding Fe-EDDHA testing interference.
- API Phosphate Test. (0, 0.25, 0.5, 1, 2, 5, 10)
$7/150 = $.05ea (@Amazon)
- Hanna Checker HI736 Phosphorus (0.0 – 0.1ppm P)
- Hanna Checker HI713 Phosphate 0.0 – 0.814ppm P
- Hanna Checker HI717 Phosphate 0.0 – 9.7ppm P
- Hanna Checker HI706 Phosphorus 0.0 – 15ppm P
- LaMotte Smart3+ 3655-SC (0.0 – 70.0ppm; MDL 5)
$22.10/50 = $0.44ea
- LaMotte Smart3+ 3653-SC (0.0 – 3.00ppm; MDL 0.05)
$38.45/50 = $0.77ea
- Hach DR900 + 8048 (0.02-2.5; MDL .02)
$31.29@Hach / 100 = $0.31ea
- Hach DR900 + 8048TNT (0.06 – 5.00)
$44.25@Hach / 50 = $0.89ea
- YSI Phosphate HR (0-100; MDL1; ±3)
$ 35.67 / 50 = $0.71ea OR 79.17 / 250 = $0.32ea
Know another way of testing for phosphate in Aquaponics? Let me know in the comments and I’ll update this post.