pH Levels in Aquaponics

Over the next few weeks the ASC Magazine will be posting sections of articles written by our writers and businesses who have contributed to the aquaponics industry and the ASC Magazine. 

This article comes from our February 2015 Edition of the magazine, Written by Vlad Jovanovic: 

Matt Bell Asked:

Hello everyone, Im fairly new to aquaponics I just ran my tests and here are my results.

Ammonia level = .25ppm

Nitrite level = 0ppm

Nitrate level = 160 ppm

PH = 7.5

Are these levels normal, or even the ballpark?

Well Matt, I suppose that would depend on what inning you are in :-) But yeah, you are definitely in the ball park. Its good that your Nitrite and Ammonia levels are at or near Zero. You may (or may not, depending on how hard your top off water is) see your pH slowly start to come down. Itll be good to get the pH below 7.

 It might also be wise to figure out what your Nitrate level actually is. By that I mean, the API Nitrate test only reads up to 160 ppm. Everything above 160 ppm pretty much reads as being 160. So your Nitrate level may actually be 240 or 500 and you wouldnt really know it, it would just read 160. 

What you can do is perform the test with twice the amount of water (10 ml instead of 5 ml). Or use the standard 5 ml of system water in the test tube, but only add half the amount of the reagents. Meaning, 5 drops from each bottle (per 5 ml of water) instead of 10 drops from each bottle. 

With either of these two methods, you are in essence doubling the upper readable limit of the nitrate tests to 320 ppm. If you perform this diluted version of the Nitrate test, and you compare the color of the test tube, to the chart...and it looks like 100ppm (for instance) this would translate to actually having Nitrates present to the tune of 200 ppm (make sense everyone?).

You can move this upper readable limit even further than 320 ppm, if need be, just by further dilutions (but hopefully that wont be necessary). Excessive nitrates are neither very healthy for our plants, or for us human to consume. 

As far as levels being normal...If we were to define what is "normal" as a matter of prevalence, or statistical occurrence; then yes, having excessive Nitrates in an AP system could be said to be "normal". It seems fairly common from what Ive seen, for AP systems to have an excess of nitrogen (and at the same time be deficient in other plant essential elements). But let us, for a moment, step away from defining what is normal only by what is common, or prevalent. Otherwise, we may say things like "obesity is normal" (because it is so prevalent), or "having heart disease is normal" (because it is so common), or "it is normal for our food to be made and modified by the worlds largest pesticide maker" (because it happens to be the condition that we find ourselves in)...and other statements like that.  

Let us instead define what is normal in terms of what would provide conditions for "normal" plant growth/health, and "normal" fish growth and health. In this case, what I think would be "normal" for an AP system to do, is to provide the conditions necessary for the near optimal genetic expression of our plants and fish (in terms of fecundity or productiveness). 

Plants Need These Things To Grow Healthy

I. What do plants need to grow?

a). Water

b). Air

c). Nutrients

d). Structure (root anchor)

e). Light

f). Adequate temperatures (both root and leaf)

g). pH at root zone (slightly acidic) 

h). *Soil *? (equates to substrate)

II. What comprises good soil (or substrate)?

a). 25% Water 

b). 25% Air

c). 45% Mineral Matter (rock, sand, silt, clay)

d). 3% - 5% Organic Matter (at various stages of decomposition)

III. Plant Essential Elements

a). Major Elements - N, P, K, Ca, Mg, S (expressed in percent %)

b). Micro Elements - Fe, Zn, Cu, Mn, B, Mo, Cl, (expressed in ppm, or mc/kg)

c). Beneficial Elements Si, Ni etc...

d). Organic molecules vs. mineral ions (microbial action vs. ionic dissociation)

e). Cations vs. Anions-Soil offers greater buffer for imbalance than water culture (show pH chart)

IV. The Role of Microbes in freeing up different plant essential elements from organic molecules...

Learn more...

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