Aquaponic Gardening

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Chelated Iron Dosing - Is there such a thing as a preventive dosing?

Is there a specific dosing of chelated iron that one can add to his system as a preventive dosing!

I know that when you see yellow leaf appearing it is normally time to add chelated iron. This said, I would like to know if there a specific dose that you can add weekly, monthly to keep your AP system in a happy iron level?

Not too much, not too high... just enough to avoid a lack of iron!

Some specs:

  1. I have a chelated iron EDDHSA 6% (Fe)
  2. Using a IBC tote with 1000 liters water +/-
  3. 2 x (4x8x12inches) Deep Floating Raft 
  4. PH is at 6.8 / 7 range

Any advices would be welcome!

Roger Pilon

Costa Rica

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That's a good observation, TC.

I'm impressed by the insights

and the scientific perspective of the participants here.

It's refreshing to see solid data and intelligent analysis

in an area that is often treated as a feel-good hobby.

@Jon Until Terri lets us know for sure I'm gonna assume (yeah, I know what they say) that mg/l is the unit (or its ppm equivalent). Based only on the weights being given in grams. (Doesn't necessarily make it so though)...

@TC Well at least this will give folks some idea about what it is their pouring onto their banana and papaya trees, that is coming out of their swirl filters :)

Good stuff Terri. 

Iron seems bloody high, considering an RAS is not being supplemented with chelated iron, and I understand tilapia feed is generally absent of iron since fish don't need it?

Whats even more frightening is the Copper! But, I'm not entirely to sure I'm able too read that info correctly...If it's mg/l-ppm, it seems out of whack, if it's % it's out of whack. I have been known to suffer from sporadic brain constipation though.

I get the deal, fish, water, and sludge all analyzed at different stages of the fish's growth, but can't work out the units/numbers? (other than comparatively relative to one another... until someone can explain it to me)?

The fish feeds will have some amounts of Iron and copper in them (this is why if the pH is lower in a system, Iron may not need to be supplemented very much, but this will depend on the source water too since some water has iron in it and mine does not!)

@ Jon and Vlad - the table represents the mean percentage of total feed nutrients found in the water column, fish flesh, and sludge. One reason why the math doesn't add up is because replicate feed samples were analyzed. The table below shows the results for the nutrient content of the feed. The authors took four 0.25 gm pulverized samples of fish feed to determined the percentage of nutrient found in each 0.25 gm sample. Because there were four samples they averaged the results to get the mean and provided the standard deviation to show the range. If we look at the percent Fe in the table below, it states that the mean percentage of iron for the four samples equals 0.1094% or 0.0002735 grams (0.1094% x 0.25 grams). The +/-  0.057 is the standard deviation (SD). To calculate the SD we add 0.057 to 0.1094 to give us the highest result and subtract 0.057 from 0.1094 to determine the lowest result. Given this we now know that the percentage of iron falls somewhere between 0.052% and 0.1668% and that the average (mean) is 0.1094%. I hope this explanation helps.

The (mean +/-S.D.) percentage (%) of nutrients in dry feed

Fe (%) 0.1094 +/- .0574
Mn (%) 0.003 +/- .0014
Zn (%) .0056 +/- .00007
Cu (%) 0.0024 +/- .000005
Ca (%) 1.74 +/- .226
Mg (%) 0.428 +/- .037
N (%) 3.40 +/- .226
P (%) 1.48 +/- .091
K (%) 0.53 +/- .0014

Thank you Terri explaining that to us. It makes so much more sense now. That's a pretty darn good fertilizer :) At fist glance it looks like those Ca-Mg-Fe-Zn-Cu ratios jive with some different generally accepted hydro formulas. (yeah, I know that's kind of a generic thing to say, since there are a lot of them, but Barry (1996), Jones (1997), Yuste/Constincar (1999) are a few that I'm at least a little familiar with)...Good stuff. Thanks Terri.


This was a pilot study using the following system design. They used RAFT troughs without plants to simulate an AP system and to shade the culture tank to limit algal growth. 

Solids were not removed from the system.  The authors assumed mineralization took place because the percentage of total phosphorus and nitrogen in the "aged" sludge samples were less than what is normally found in fresh sludge. Mineralization is one reason why the nutrient content of sludge is high. The microorganisms that break down the organic waste usually settle out and becomes part of the sludge. As with plants and fish, microorganisms also require macro/mirco-nutrients to sustain life. The following shows the composition of a single cell:


Water = 70 – 90%
Dry Mass = 10 - 30%

Dry Mass Composition
(Organic fraction)
Carbon = 45 – 55%
Oxygen = 16 – 22%
Nitrogen = 12 – 16%
Hydrogen = 7 – 10%
Phosphorus = 2 – 5%
Sulfur = 0.8 – 1.5 %
Potassium = 0.8 – 1.5%
Sodium = 0.5 – 2.0 %
Calcium = 0.4 – 0.7%
Magnesium = 0.4 – 0.7%
Chlorine = 0.4 – 0.7%
Iron = 0.1 – 0.4 %
All others (including trace elements) = 0.2 - 0.5%


The following table shows the the nutrient accumulation in the water during the 3 week test period.

Was there any sort of filtration?  Other than the surfaces of the tank and troughs on top?

How were they collecting the sludge?

TC, in the study it says that they scooped the sludge right out of the raft, and their was nothing described in the wasy of additional filtration. Just a FT, rafts, and pump.

Feed was  commercial floating pellet (Car-Gill Company;

24% protein

6% fat



I wonder how Trout Chow or Aquamax type higher protein feeds would effect these numbers?

Heck, I've read how different types of fish will provide you with different numbers in the waste.

All interesting.  Did they say how often they were scooping the sludge out?

Yeah, and then there's that...

Nope. It just says... "the sludge (water, uneaten food, and bacterial bio-mass) was gathered from each of the hydroponic troughs and..."  two samples 300 ml each, homogenized, dried at 70 degrees weighed by gravimetry....

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