This is part of a series on Aquaponic Water Testing.

Iron is one of the most common deficiencies in Aquaponics systems. The main symptom of a deficiency is interveinal chlorosis on the newest leaves of the plant. Many other deficiencies cause interveinal chlorosis, so relying on visual identification can be hard, especially for inexperienced growers.

Aquarium test kits, like the Seachem MultiTest Iron, should be avoided if possible. They lack the ability to accurately check for chelated iron. However, they will answer the question “Is there Iron?”

I own and use the Hanna Checker HI721.

If you use Fe-EDDHA, or Fe-HBED in your system, beware test interference. The YSI MR test is the most accurate test I’ve found. It separates out the Iron Reducer and the phenanthroline reagent, allowing for the photometer to be zeroed in between the two steps.

1. Seachem MultiTest Iron
   $13.09 / 75 = $0.17ea
   
2. Hanna Checker HI721 (0.00 – 5.00; MDL 0.01; Resolution 0.01)
$49.13@Amazon Meter + 6 tests.
   $6/25 refills=$0.24 ea
   
3. LaMotte Smart3 + 4315-H (0.0-10.0, MDL 0.05)
   $37 / 100 = $0.37ea
4. Hach DR900 + 8008 (0.02 – 3.0; Resolution = 0.021)
   $21.95@Hach / 100 = $0.22ea
    + 
5. YSI 9500 + Iron MR (0 – 5.0; MDL 0.02)
   $46 / 50 = $0.92ea OR $104.40 / 250 = $0.42ea
6. YSI 9500 + Iron HR (0-10.0; MDL 0.05)
   $23.49 / 50 = $0.47ea OR $46.98 / 250 = $0.19ea

Have I missed an Iron test that would work for Aquaponics? Let me know in the comments and I’ll update this page.

This article on Magnesium Testing is part of a series on Aquaponic Water Testing.

Magnesium is important for photosynthesis in plants. It forms the center of the chlorophyll molecule. If deficient, plants will begin breaking down chlorophyll in older leaves, leading to the symptom of Interveinal Chlorosis in those older leaves.

Beware, Zinc deficiency produces the same symptoms. Ensure your magnesium levels are correct before considering Zinc. If you have interveinal chlorosis in older leaves and your Mg²⁺ levels are fine, take the time to test for zinc.

Hoagland suggests a Magnesium level of 48 ppm. The ratio of Magnesium to Calcium is important as well.

Measuring Magnesium

Your magnesium level can be measured, or calculated. Calculation is the traditional method. The Red Sea kit is an example of a direct titration, while the YSI Magnicol is a colorimetric test.

1. Red Sea Magnesium Pro (Resolution 20ppm)
   $30.36 / 100 = $0.30ea (@Amazon)
   
2. YSI Magnesium Magnicol (0-100; MDL 2; ±1)
   $38.40 / 50 = $0.77 OR $62.64 / 250 = $0.25

Calculating Magnesium.

Total Hardness = Calcium Hardness + Magnesium Hardness + divalent metal hardness.

We can safely ignore (and some tests specifically mask out) metal hardness in our tests.  That means if we test for Total Hardness and Calcium (or Calcium Hardness), we can calculate Magnesium Hardness. When calculating, your results will only be as accurate as your source measurements. Use a higher resolution method for the Calcium test, such as with the Hach Digital Titrator, or pool chemicals in order to get accurate results here.

Most calcium tests give the results in the form of Ca²⁺. In order to convert that to Calcium Hardness, we multiple it by 2.5.

Total Hardness = (Ca²⁺* 2.5) + Magnesium Hardness

Magnesium Hardness = Total Hardness – (Ca²⁺* 2.5)

Once we do our subtraction, we can convert Magnesium Hardness to Mg²⁺ by dividing by 4.1

Mg²⁺ = Magnesium Hardness / 4.1

Know of a different way to test for Magnesium in an Aquaponic system? Let me know in the comments and I’ll update the post.

This is part of a series on Aquaponic Water Testing.

General Hardness is the sum of Calcium, Magnesium, Iron, Aluminum, Manganese, and any other divalent metal ion. In Aquaponic systems, generally only Calcium and Magnesium contribute meaningfully to General Hardness.

General Hardness is reported in 3 different ways; degrees (dGH), ppm, and grains per gallon (gpg). We are most concerned with ppm,  but dGH is a common measure, and you may see grains per gallon listed on a water quality report.

1dGH = 17.85ppm CaCO₃
1gpg = 17.12ppm CaCO₃

A common mistake I see online is people see that they have a GH reading of 100ppm, and think that means they have calcium of 70 and magnesium of 30.

GH (as ppm CaCO3) = CaCO3+ MgCO3 + FeCO3 + MnCO3

Because our water tests give us Calcium results as Ca2+, not CaCO3, we use a conversion factor to make the equation work.

GH (as ppm CaCO3) = Ca²⁺ * 2.5 + Mg²⁺ * 4.1 + Fe²⁺ * 1.79 + Mn²⁺ * 1.8

Someone with a GH reading of 100ppm could have a Calcium reading of 40, a Magnesium reading of 24, or some combination in the middle.

General Hardness Testing

Testing for General Hardness is done two ways: Titration, and Colorimetry.  Both methods work, although Colorimetry has problems with <10ppm values.

Titration based:

1. API GH and KH Test Kit 1dKH resolution = 17.86ppm resolution
   $5.39 (@Amazon)
   Number of tests depends on your KH and GH levels, so cost per test varies
2. Hach Digital Titrator + 8329 Sequential Hardness (10-4000)
   This sequential test provides Total, Calcium, and Magnesium Hardness
   $159@Hach + $84.95@Hach / 100 = $0.85ea+
3. Taylor Test K-1503. 2ppm or 10ppm resolution
   $60 with shipping as a kit.
4. Taylor Test – based on K-1722. 10ppm resolution
   Order reagents:

   R-0854-C & R-0012-C
   and follow instructions here https://www.taylortechnologies.com/en/Image/GetDocument/725

Colorimeter based:

1. Lamotte Smart3 + 4309-J (10-450ppm)
   $30 / 100 = $0.30ea

This is part of a series on Aquaponic Water Testing.

Calcium is essential for plant health. Deficiency symptoms include death of growing points, abnormally green foliage, premature shedding of blossoms/buds, and weakened stems. Blossom end rot and lettuce tip burn are usually more issues of inadequate transpiration than calcium deficiency.

Hoagland suggests a level of 200ppm. I aim for 100-150ppm.

Testing for Calcium

Testing for Calcium is done three ways: Titration, Colorimetry, or Ion Specific Probe.  Titration is the classical method, but YSI + Hanna have a colorimetric method available. The Horiba LAQUAtwin Ion Specific Probe provides fast results, but requires calibration at every use.

Some tests give results in Calcium Hardness (CaCO₃). Since we’re interested in results in ppm Ca²⁺, divide Calcium Hardness results by 2.5.

1. API Calcium test (Resolution = 20ppm Ca²⁺, dropwise titration) $6.29@Amazon / 75 = $0.08 ea
   The API test is listed for Saltwater aquariums, and if you call API they will tell you it can only be used on Saltwater aquariums. I have tested it with freshwater samples of known concentration, and have found that it does work, but is difficult to read. Many aquaponic systems that are not actively supplementing calcium will see the color change on the first or second drop. In order to see the change, look through the top of the test tube, and make sure you have a white piece of paper as your background. The color change is light pink to light blue, so I recommend looking for a change from “slightly warm” in color, to “slightly cool” in color.
2. Taylor K-1770 (Resolution = 4ppm Ca²⁺, dropwise titration)
   $27.28@Amazon / 22 = 1.24ea
   2oz Refills $15.65 = $0.17ea
   Taylor tests are very common in the pool industry. If you have a way of measuring 25ml of water, you can purchase the reagents  (R-0010, R-0011L,  R-0012) for as little as $15.65 at local pool supply companies. Retail stores like Leslies Pool will charge as much for the reagents as the kit would cost, so be careful. The instructions specify resolution as 10ppm CaCO₃, which is equivalent to 4ppm Ca²⁺. That’s 5x better than the API test, and this test is easier to read.
3. Hach Digital Titrator + 8204 (40 – 1600ppm Ca²⁺ )
   Titrator: $159@Hach +
   Reagent 8204: $49.95@Hach / 100 = $0.50 ea
   Results are giving in ppm CaCO₃. Divide by 2.5 to get results in Ca²⁺. Resolution is 10x higher than the Taylor K-1770 test, but that increase in resolution is unnecessary in non-research systems.
    + 
4. Hanna Checker HI758 (200-600ppm, 1ppm)
   $41.65 Meter + 15 tests.
   Refill $21 / 25 = $0.84ea
   Sadly, I mention this Hanna Checker mostly to dissuade you from purchasing it. Notice the minimum value is 200. Most of the time in Aquaponics, we will be well below that 200 number.
5. YSI Calcium Hardness Calcicol (0-200 Ca²⁺; MDL 2; ±2)
   $30.45 / 50 = $0.61ea OR 73.08 / 250 = $0.29ea
6. Horiba LAQUAtwin Calcium Ion Meter (40-4000 ppm) $352@Amazon + ($100sensor+ $44calibration)/1500 = $0.10ea The sensor on this Ion Meter should be good for approximately 1500 readings, assuming you rinse it with distilled water after every use. It also needs calibration before every test run. If you have a number of separate systems, this item will save you time and money in the long run.

Know of another way of testing for calcium in aquaponics? Let me know in the comments and I’ll update this post.

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.

1. API Phosphate Test. (0, 0.25, 0.5, 1, 2, 5, 10)
   $7/150 = $.05ea (@Amazon)
2. Hanna Checker HI736 Phosphorus (0.0 – 0.1ppm P)
3. Hanna Checker HI713 Phosphate 0.0 – 0.814ppm P
   $46.38 (@Amazon)
4. 
Hanna Checker HI717 Phosphate 0.0 – 9.7ppm P
5. Hanna Checker HI706 Phosphorus 0.0 – 15ppm P
6. LaMotte Smart3+ 3655-SC (0.0 – 70.0ppm; MDL 5)
   $22.10/50 = $0.44ea
    + 
7. LaMotte Smart3+ 3653-SC (0.0 – 3.00ppm; MDL 0.05)
   $38.45/50 = $0.77ea
    + 
8. Hach DR900 + 8048 (0.02-2.5; MDL .02)
   $31.29@Hach / 100 = $0.31ea
    + 
9. Hach DR900 + 8048TNT (0.06 – 5.00)
   $44.25@Hach / 50 = $0.89ea
    + 
10. 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.

This is part of a series on Aquaponic Water Testing.

Alkalinity, along with CO2 levels, drives the pH level in aquaponics systems. Alkalinity is also required for the wee little beasties that convert ammonia to nitrite and nitrate. That means that maintaining the proper type and level of alkalinity is very important.

At a minimum, you would want an alkalinity of 20, or 1.5dKH.  Alkalinities can range upwards of 300-400ppm, as long as the proper type of alkalinity is maintained.

There are two types of Alkalinity, Carbonate  & Bicarbonate . Add them together and you have Total Alkalinity. As long as your system pH is under 8.3, you only have Bicarbonate Alkalinity, which is good. Bicarbonate alkalinity actually struggles to bring the pH up to 7.8. That is why I recommend never using Hydroxides, and only using Calcium Carbonate, never Potassium Carbonate.

Alkalinity is pretty easy to check. I use both the API KH test kit, and the Hanna Checker HI775. The geek in me enjoys the ppm resolution of the Hanna Checker, the miser in me knows the API test costs 1/15 the amount:

1. API GH and KH Test Kit 1dKH resolution = 17.86ppm resolution
   $5.39
   Number of tests depends on your KH and GH levels, so cost per test varies
2. Hanna Checker HI775 (0-500ppm range; 1ppm resolution)
   $49 / 25 = $1.96ea (@Test Equipment Depot)
   Refills $19 / 25 = $0.76 ea
   
3. Hach Digital Titrator +8203
   $159@Hach + $66.95@Hach / 100 = $0.67ea
   +
4. Lamotte Smart3 + 4318J (10-200ppm)
   $37.00@GlobalWater / 100 = $0.37
    + 
5. Hach DR900 + 8030 (0.05 – 4.00)
   $65.95@Hach / 100 = $0.66ea
    + 
6. YSI 9500 + AlkaPhot (10-500ppm)
   $30.45 / 50 = $0.61ea OR $64.38 / 250 = $0.26