Your plants need Nitrogen to grow. Nitrogen comes in many forms – Ammonia, Nitrite, and Nitrate. We need to know how much Nitrogen is in our Aquaponics system. We could perform a persulfate digestion to get TN (Total Nitrogen), but in a properly running Aquaponics system, the majority of Nitrogen will be in the form of Nitrate.

When setting up a new system, or making major changes (such as a grow bed cleaning, adding new fish, or changing feed rates) I recommend testing Ammonia and Nitrite as well as Nitrate.

The Nitrogen Cycle

In the nitrogen cycle, bacteria break down the nitrogenous compounds (fish waste & uneaten food). First, Ammonia is changed into Nitrite. Then, Nitrite is changed into Nitrate. Both Ammonia and Nitrite are dangerous to fish, but Nitrate is fairly well tolerated by most species.

Testing for Nitrate in Aquaponics

1. API Nitrate Test (0, 5, 10, 20, 40, 80, 160 ppm)  $8.92 / 90 = $0.10 per test.
2. LaMotte Smart3 + 3689-SC. Zinc Reduction. (0.0-60.0 ppm) $33/50 tests = $0.66 per test.
3. Hach DR900 + 8039 Nitraver 5 Cadmium Reduction. (0.3 – 30pppm)  $50.39 / 100 tests = $0.54 per test
4. YSI 9500 + NitraTest. (0.0 – 20.0 ppm) $155/200 = $0.77 per test OR $60/50 = $1.20 per test

This is part of a series on Aquaponic Water Testing

In an Aquaponic system, we have to rely on some sort of chelate to keep iron available to our plants. Without a chelator, iron is only stable at pH levels below 4. Fe-EDTA is the most common form of chelated iron found, but EDTA is only stable under acidic conditions and it’s breakdown products are phytotoxic.

Suitable chelator choices include Fe-DTPA, Fe-EDDHA, and FE-HBED. Fe-DTPA is a great iron chelate product, but it exhibits rapid photodegredation. One study reported a half life of 30 minutes in full sunlight. When I used Fe-DTPA, I found my iron levels would drop from 2.5ppm to 0.0ppm within 3 days. Since iron chelates are expensive, having to re-dose iron on a regular basis can end up being a large cost. If you are able to keep your water dark, Fe-DTPA may work for you.

The alternatives are Fe-EDDHA, and Fe-HBED. Fe-EDDHA is stable up to a pH of 10, and Fe-HBED is stable up to a pH of 12! Both of these products will stain your water slightly red.

Above:No, that’s not red wine, or kool-aid. It’s iron chelate! From left to right Fe-HBED, Fe-EDDHA, Fe-DTPA. All at 20ppm.
Below: what Fe-EDDHA looks like at 0.5, 1.0, 1.5, 2.0, and 3.0ppm concentrations

If this color was “permanent”, colorimeters/spectrophotometers would just compensate for it when you zero out the meter. Unfortunately, certain circumstances cause the pink hue to disappear mid-reaction. The can be caused by the pH going high, and the Fe-EDDHA being degraded, or by the iron being reduced or complexed with another molecule. So far, the problem has been noted with:

• Nessler based Ammonia Tests
• Molybdenum blue based Silica and Phosphate tests
• Iron tests

Interference with Iron Tests:

Most iron tests are phenanthroline  based. An Iron reducing agent is introduced, and then the iron reacts with  phenanthroline to cause a red hue which the photometer reads. Most tests have the reducing agent and phenanthroline combined into one packet. If you were to use a YSI Mid-Range Iron test, you would notice it had two reagents. The first reagent is the iron reducer. After adding the iron reducer, the pink color disappears from the sample. If we zero the meter at this point, then continue the test, we end up with the correct result.

If the meter is zeroed before the iron reducer is added, the pink hue is counted against the further color development. This leads to a reported value that is lower than actual.

There are a few ways to deal with this interference.

1. Treat your sample blank with Sodium Hydroxide to raise the pH and destroy the Fe-EDDHA. Unfortunately, phenanthroline is only stable up to a pH of 9.0, so you can’t treat the sample.
2. Treat your sample blank with Sodium Dithionite, an Iron reducing agent. Sodium Metabisulfite is much easier to find and will also work, but will requires 2x as much compared to Sodium Dithionite.
3. Treat your sample blank with RoVer, an Iron reducing agent.
4. Use distilled water as your sample blank, accepting that this will cause errors.
5. Apply a calculated correction to your result.
6. Stop using Fe-EDDHA/Fe-HBED.

My recommendation is #3 – using RoVer. It’s concentrated, and works like a charm.

Interference with Ammonia Tests

During a Nessler based Ammonia test, the pink hue of Fe-EDDHA disappears after the photometer has been zeroed. This leads to “Inverted Cuvette” errors or bad results.

Interference with Molybdenum blue based Silica and Phosphate Tests

During a Molybdenum blue based Silica or Phosphate test, the pink hue of Fe-EDDHA disappears after the photometer has been zeroed. In testing, the Hach 8048 TestNTube was not susceptible  to interference.

With Fe-EDDHA, it is possible to increase the pH and destroy the EDDHA molecule. 10 drops of Sodium Hydroxide (1N solution, which can be found in the API Calcium Test, bottle 1) will raise the pH enough.

Fe-EDDHA and Fe-HBED Spectral Analysis

In Aquaponics, Dissolved Oxygen (DO) is extremely important. We all know that fish require dissolved oxygen in order to breathe. But plant roots require adequate dissolved oxygen to survive as well. Even the beneficial bacteria in our filters need oxygen. Having a way of testing for dissolved oxygen lets you make sure you have enough aeration for your fish and plants to thrive. It will also let you answer questions like “How much oxygen do airstones put in my system?” or “Does my system need more aeration?”

Overview of Dissolved Oxygen Testing Options

Dissolved Oxygen testing can be done with a chemical test, electrochemical sensor, or through an optical based sensor.

Chemical testing methods are accurate, and don’t need calibration. The up-front cost can be low, but at $0.51 – $1.20 per test the cost will  add up. The main disadvantage of the chemical methods is you only learn the DO for where you sampled. Comparing DO levels in a tank, sump, and raft bed would need at least 3 separate tests.

With a sensor based meter, you can simple move the DO probe from area to area and wait for the readings to stabilize.

Electrochemical sensors come in two varieties: Galvanic and Polarographic. Polarographic sensors last longer, but require a 5-15 minute warmup. Galvanic sensors work immediately, but won’t last as long as a Polarographic model, as they age even when the meter is  turned off. Luckily both sensor types can be maintained. In continuous use, probe membranes last 2-8 weeks. Plan on spending up to $100 a year in maintenance costs.

Optical Dissolved Oxygen, or Luminescent Dissolved Oxygen probes have the advantage of requiring very little maintenance. The sensor caps should be replaced every year (approx $100), but there are no membranes, special fluids, calibrations, or storage constraints to worry about.

My Opinion

I use a Hach HQ30d meter with Rugged LDO probe. If you are careful, you can buy a similar setup on eBay for around $200. Assume that the sensor cap will be past the calibration expiration date. A new sensor cap is $108, but the sensor will continue to work with an expired cap and you can check the accuracy by performing a calibration. Make sure the eBay vendor states that the probe connects to the meter, and displays a reading.  (PS: Need help figuring out if an eBay auction for a Dissolved Oxygen meter is any good? Ask in the comments. I’ll try to reply individually by email, and won’t post the comment until the auction ends, so nobody snipes it from you.)

If you’re not comfortable with used equipment and are on a budget, the Milwaukee MW600 is a great deal (149@Amazon).

The only real duds here are the chemical tests.

Chemical test / Winkler Titration

1. Hanna HI3810 (0.0-10.0; Resolution 0.1)
   $56 / 110 = $0.51ea
   
2. LaMotte 5860-01 (0.0 – 10.0; Resolution 0.2)
   $52 / 50 = $1.04 ea
   
3. Hach Digital Titrator +8332 (1 – 10 mg/l)
   $159@Hach + $84@Hach
    + 

Chemical Test / Photometric

4. LaMotte Smart3 + 3688-SC (0.0-10.0; MDL 0.6)
   $40 / 100 = $0.40 ea
5. Hach DR900 + 8166 (0.3 – 15.0)
   $30 / 25 = $1.20 ea
   This is the easiest chemical dissolved oxygen testing method. Individual vacuum filled ampules have the reagent in them – just snap the neck under-water to fill the ampule, and put it into the meter to read.
    + 

Electrochemical

6. OxyGuard Handy Polaris Galvanic $934
   The original handheld, waterproof Dissolved Oxygen Meter. The OxyGuard meters are reported to need less maintenance than other electrochemical probes.
   
7. YSI Pro20 Polarographic or Galvanic $947@Amazon
   
8. YSI 550A Polarographic $759@Amazon
   
9. YSI EcoSense 200A Polarographic $495@Amazon
   
10. American Marine Pinpoint II Polarographic $229@DrFostersSmith
    The Pinpoint II and Milwaukee MW600 are roughly equivalent devices. They both require a two-point calibration (more expensive units don’t need zero calibration) and while the probes are waterproof, the meters are not. If you’re the type to knock something into the tank… neither of these units will survive that.
    Don’t forget to purchase zero-calibration solution as neither meter comes with it.
    
11. Milwaukee MW600 Polarographic $149@Amazon
    Update: Milwaukee now ships these units with calibration instructions that don’t require zero-calibration solution! I’d recommend this unit over the Pinpoint II because of that. There is a great video showing how to calibrate and install membranes on this unit here.
    

Optical

12. Hach HQ30d + Rugged LDO Sensor
    Meter: $750@Hach +
    Probe: $750@Hach +
    Sensor Cap: $108/yr@Hach
     +  + 
13. YSI ProODO
    Meter: $604@Fondriest +
    Probe: $556@Fondriest +
    Sensor Cap: $87/yr@Fondriest
     +  + 

Know of, or use another method of testing for dissolved oxygen in Aquaponics? Let me know in the comments and I’ll update this post.

This is part of a series on Aquaponic Water Testing.

Nickel is interesting. Unless you are growing pecans, or multi-generational wheat, Nickel will probably not be needed in your Aquaponic system. In Hydroponics: A Practical Guide for the Soilless Grower By J. Benton Jones, Jr ($72 @Amazon), a level of 0.057ppm Nickel has been proposed.

Sufficient nickel for plants should be present as trace in other supplements, such as Azomite or Maxi-Crop.

You may want to test for Nickel if you have used an Inconel based heating element and have unexplained fish deaths.

Testing for Nickel

I have only found one visual method that even comes close to the .05ppm range we are interested in. If you truly want to measure your Nickel levels, Hanna and Hach have excellent methods.

1. LaMotte 7802 (.5, 1,2,3,4,5,7.5,10)
   $140 / 20 = $7ea
   
2. Hanna Photometer HI96740 (0.000 – 1.000ppm; Resolution 0.001ppm)
   Meter: $196@Amazon
   Reagent: $137@CapitolScientific / 50 = $2.74ea
   
3. LaMotte Smart3 + 3663-SC (0.0-8.0, MDL 0.15)
   $143.50 / 50 tests = $2.87ea
   With a Minimum Detection Level of 0.15ppm, nearly 3x our suggested level, this nickel test method isn’t appropriate for Aquaponics.
4. Hach DR900 + 8150 (0.006-1.000; resolution = 0.006)
   $141@Hach / 100 = $1.41ea
    + 
5. YSI Nickeltest (0-10; MDL 0.12)
   $73.08 / 50 = $1.46 OR $175.74 / 250 = $0.70
   With a Minimum Detection Level of 0.12, YSI’s Nickeltest will be of limited use, except in diagnosing Nickel poisoning.

Supplementing Nickel

Bad news. The National Organic Program does not recognize Nickel as essential. Therefore, any nickel supplementation is against organic rules. Nickel Nitrate or Nickel Sulfate are easily available.

Know of, or use another method of testing for Nickel in Aquaponics? Let me know in the comments and I’ll update this post.

This is part of a series on Aquaponic Water Testing.

Another heavy metal, Molybdenum is necessary and safe to add to Aquaponic systems. Hoagland suggests 0.02ppm, a level we can safely accommodate since the PNEC_Aquatic for Mo is 12.7ppm.

Molybdenum deficiency will include symptoms of nitrogen deficiency. An upward cupping of leaves, and mottled spots turning into interveinal chlorosis may be present. Cauliflower can exhibit a whiptail appearance. While rarely seen, molybdenum toxicity is easy to visually diagnose – leaves will turn a very brilliant orange.

Testing for Molybdenum

While I am listing one color comparator test, most methods that provide the resolution we require will require a photometer/colorimeter.

1. Hanna HI96730 Portable Photometer (0.0-40.0; Resolution 0.1)
   $209@Amazon meter + $75 / 100 = $0.75ea
2. Hach MO-LR (0.25 – 3 mg/L)
   $121 / 100 = $1.21ea
   
3. Hach DR900 + 8169 (0.02 – 3.00 mg/L; Res 0.02)
   $57.95@Hach / 100 = $0.58ea
    + 
4. Hach Colorimeter II Moly (0.02 – 3.00 mg/l)
   
5. YSI Molybdate LR (0-15; MDL 0.2)
   $35.67/50 OR $73.95/250
    + 

Know of, or use another method of testing for Molybdenum in Aquaponics? Let me know via the comments and I’ll update this post.

This is part of a series on Aquaponic Water Testing.

Zinc is necessary for plant growth, but  only small amount are needed. A deficiency can show itself as interveinal yellowing and pitting on younger leaves, leading to advanced interveinal necrosis. Leaves may also become smaller with shortened internodes.

Hoagland suggests a zinc level of 0.05ppm. That number should be safe in Aquaponic systems, but anything over that would start to cause problems with invertebrates.

Testing for Zinc

Because of the extremely low levels we are measuring, there are no visual methods available to us. Currently, the Hanna HI96731 is a great deal from Amazon if you don’t own a multi parameter colorimeter.

1. Hanna HI96731 (0.00 – 3.00; Resolution 0.01)
   Meter: $60@Amazon
   Reagents: $48@eSeasonGear / 100 = $0.48ea
   I have this meter. It’s fairly easy to use, but in order to use the meter you’ll need reagents, and a 20ml graduated mixing cylinder.  
   
2. LaMotte Smart3+3667-01-SC (0.00-3.00; MDL 0.05)
   Reagents: $112 / 50 = $2.24ea
    + 
3. Hach DR900 + 8009 (.01-3.0; Resolution 0.013)
   Reagents: $58.95@Hach / 100 = $0.59ea
    + 
4. YSI 9500 + Zinc (0-4.0; MDL 0.02)
   $46.11 / 50 = $0.92ea OR 120.06 / 250 = $0.48ea
    + 

Zinc Safety

Adjusting Zinc Levels

National Organic Program states: Zinc carbonate, zinc oxide, zinc silicate, and zinc sulfate may be used to correct a documented zinc deficiency., 205.601(j)(6)(ii) As plant or soil amendments… Micronutrients—not to be used as a defoliant, herbicide, or desiccant. Those made from nitrates or chlorides are not allowed. Soil deficiency must be documented by testing.

I use zinc sulfate. I ordered a 1lb bag from Ebay, and was sent a 5 lb bag instead. At my current rate of usage, that should last me several hundred lifetimes.

Know of another way to test for Zinc in Aquaponics? Or have a different supplement regime? Let me know in the comments and I’ll update the page.

This is part of a series on Aquaponic Water Testing.

Silica can strengthen cell walls,help regulate uptake of toxic elements, increase heat tolerance, and slow transpiration. That leads to more upright plants with increased disease and insect resistance. Silica is not necessary for all plants, but may be beneficial to some species. Research has shown that Tomato plants require between 5 – 20 ppm silica for normal growth (link).

In an aquaponic system, I like to aim for a level of 30ppm SiO2.

Testing for Silica

The first two entries are both “Aquarium level” test kits. Use them with caution. I have and use the Hanna Checker HI770.

If you use Fe-EDDHA or Fe-HBED, you will experience interference.

1. Seachem Multitest Silicate (0-25)
   $19.08@Amazon / 75 = $0.25ea
   
2. Salifert Silicate Profi-test (0-30)
   $21.99 / 60 = $0.37ea
   
3. Hanna Checker HI770 (0-200; Resolution 1ppm)
   $51.05@Amazon meter + 6 tests.
   Reagents $34@Amazon / 25 = $1.36ea
   
4. LaMotte 4463-01 (5, 10, 20, 30, 40, 60, 80, 100)
   $70.16 / 50 = $1.40ea
5. LaMotte Smart3 + 3687-SC(0.0-75.0)
   $40.66@GlobalWater / 50 = $0.81ea
    +
6. Hach DR900 + 8185 (1 – 75)
   $72.95@Hach / 100 = $0.73
   +
7. YSI 9500 + Silica HR (0-150; MDL 0.5)
   $56.55 / 50 = $1.13 OR $139.20 / 250 = $0.56

Know of another way of testing for Silica in Aquaponics? Let me know via the comments and I’ll update this page.

This is part of a series on Aquaponic Water Testing.

Copper is necessary in an aquaponics system in small amount for proper plant growth.

Copper deficiency symptoms include leaves curling and bending downward, a light chlorosis and loss of turgor in young leaves, sunken necrotic spots on leaves, and small leaves.

Hoagland suggests a level of 0.02ppm, which should be safe for aquatic organisms given that the PNEC_Aquatic is 0.03ppm.  Most fish can handle larger amount of copper, but invertebrates such as shrimp, crayfish, and snails are very sensitive. Plant roots may start to experience damage at levels >0.1ppm. At 0.3ppm copper begins to inhibit the bacteria responsible for ammonia and nitrite oxidation.

Testing for copper

Most visual colorimetric tests do not have enough sensitivity, however the Taylor K-1730 is on the borderline, and will allow basic copper determination. The most accurate copper tests use the Porphyrin method (Such as Hach 8143), which does not form a strong visual indicator.

1. Taylor Technologies K-1730 (0, 0.05, 0.15, 0.3, 0.5, 0.7, 1.0)
   $25.15@Taylor
2. Hanna HI3856 (0.00, 0.05, 0.10, 0.15, 0.20, 0.25 ppm)
   NOT AVAILABLE. Manufacturer contacted but even they don’t know why they stopped making it.
3. Hanna HI96747 (0.000 – 1.500; Resolution 0.001)
   $188 meter @Amazon + $98 @ESeasonGear / 100 = $0.98ea
   
4. LaMotte Smart3 + 3640-SC (0.00-3.50; MDL 0.04)
   $27.75 / 100 = $0.28ea
   + 
5. Hach DR900 + 8506 (0.04 – 5.00)
   $38.75@Hach / 100 = $0.39ea
    + 
6. Hach DR900 + 8143 (0.000 – 0.210)
   $190@Hach / 100 = $1.90
   The _most_ accurate method available.
    + 
7. YSI Coppercol (0-5.0; MDL 0.03)
   $48.72 / 50 = $0.97ea OR $126.15 / 250 = $0.50ea

What if my copper is too high?

If your copper level is above where you want it and you have sensitive organisms such as shrimp or crawdads, you have two options: Water changes, or CupriSorb. CupriSorb is expensive, but may be regenerated once it’s full of copper.

If your copper level is too high, it’s important to investigate why. If your source water is high in copper you could use a R/O machine or treat makeup water with a bag of CupriSorb.

What if my copper is too low?

Copper Sulfate or Copper Nitrate are the most commonly used forms of copper. Be very careful as you’ll be measuring tenths of grams if you decide to supplement.

Know of a different way to test for Copper in Aquaponics? Let me know in the comment section and I’ll update this post.

This is part of a series on Aquaponic Water Testing.

Potassium is very important to plant growth. A Potassium deficiency will cause older leaves to appear chlorotic, and uneven ripening(if at all) in fruit. Unfortunately, fish require no dietary Potassium. Therefore most fish feed is not supplemented with Potassium.

How much Potassium?

Hoagland suggests a plant “ideal” of 235ppm. Another approach is to aim for a value 2/3 of your nitrate levels, or twice your phosphate levels. Excess Potassium may lead to deficiencies in Magnesium, Manganese, Zinc, and/or Iron.

 Potassium Testing Methods

There are two methods of testing for Potassium; turbidity based tests, or using an Ion Specific Probe. I have the LaMotte Double Tube test kit, and it works, but is cumbersome. I have also used the YSI method and love the ease and rapidity of the test. It does have a low range (0-12ppm), I usually diluted my sample 10 to 1 which increases that range to 0-120ppm.

1. LaMotte 3138-01 Double Tube (0, 6, 7, 10, 20, 30, 40, 50)
   $65.20 / 100 = $0.65ea
   I have and use this double tube setup. If my potassium is >50, I could re-run the test after diluting the sample with distilled water, but often don’t.
   
2. Hanna HI96750 Portable Photometer (10-100; Resolution 1)
   Meter: $176 / $196@Amazon
   Reagent: $85 / 100 = $0.85ea
   
3. LaMotte Smart3 + 3639-SC (0-10.0, MDL 0.8)
   $59.65 / 100 = $0.60ea
4. YSI YPM189 (0-12; MDL 0.5)
   $35.67 / 50 = $0.71ea OR $79.17 / 250 = $0.32ea
5. Horiba LAQUAtwin Potassium 39-3900ppm
   Meter: $320@Amazon +
   Sensor: $127@Amazon / 1500 = $0.08ea
   Requires calibration before every use.
   

Potassium Supplementation

There are a number of chemicals we can use to supplement the Potassium in our Aquaponics systems. I use MonoPotassium Phosphate, Potassium Nitrate, Potassium Bicarbonate, and Potassium Silicate. I save my banana peels for my compost bins.

1. Potassium BiCarbonate
2. Potassium Hydroxide
3. Potassium Nitrate
   I love potassium nitrate. For every 3ppm Potassium added, you also get 1ppm Nitrate.
4. Potassium Sulfate
   Potassium Sulfate works, but since plants don’t use as much sulfate as potassium, you could end up with sulfate issues.
5. Mono Potassium Phosphate (MKP)
6. Potassium Silicate
   Allowed in organic production as Sil-Matrix, an aqueous Potassium Silicate, as a “pesticide”.
7. Banana Peels
   Not recommended. The number of banana peels needed means your growing media would be banana peels, not rocks.

Do you know of a different way of testing for Potassium in Aquaponics? Let me know in the comments and I’ll update this page.

This is part of a series on Aquaponic Water Testing.

Boron deficiency can be seen as interveinal chlorosis of upper leaves, brittle leaves, and stunted growth. On celery, Boron deficiency is easily noticed as “cat-scratch” marks on the plant stems.

Boron levels in Aquaponics

Hoagland suggests a Boron level of 0.5ppm. Levels above 1ppm can be toxic to plants. Because of this, I greatly recommend testing your Boron levels before you supplement. Supplementing Boron without testing is a recipe for disaster!

Testing for Boron in Aquaponics

Unless you have a LaMotte Smart3 Photometer, the Hanna HI38074 is your only bet for measuring boron levels yourself.

1. Hanna HI38074 (Resolution = 0.2ppm)
   $65/100 = $0.65ea
   I use this test kit, and if you can follow directions, you should be able to complete this titration. Includes a digital pH meter!
   In this titration, one drop < 0.2ppm. That means if your result is 3 drops, your Boron reading is less than 0.6ppm.
   
2. Taylor Technologies K-1541 (Resolution = 0.2ppm)
   $180.50
3. Salifert Boron Test (Resolution = 0.5ppm)
   $29.46/25 = $1.18ea
   For reef aquaria only, expects pH 8-8.6. Don’t use for Aquaponics!
4. LaMotte Smart3 + 4868 (0. 0-0.80, MDL .05)
   $102@GlobalWater /50 = $2.04ea
    +
5. Hach DR900 + 10252 (2 – 50; Resolution = 2.2ppm)
   $289.95@Hach / 100 = $2.90ea
   Gaseous Hydrochloric Acid forms when mixing reagent. Use Caution! Also, this method only has sufficient resolution when used with a spectrophotometer, such as the DR1900.
   +
6. Hach DR1900 + 8015 (0.2 – 14.0)
   $289.95 / 100 = $2.90ea
   Gaseous Hydrochloric Acid forms when mixing reagent. Use Caution!
   + 
7. YSI 9500: Method discontinued

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