Every quarter or so, I share the nutrient analysis of the aquaponics system water. I try to test the system water every two weeks or so. This is the 4th report. Using a photometer, I can get a handle on what is going on in our water and that’s been amazingly helpful. It’s true, you really do have to measure in order to manage. As I mentioned in my last report, sharing this information helps us all to see how one system is performing. It is my hope that this will inspire others to share system info so that we can compare notes and contribute to a healthy aquaponics industry.

So what’s been going on since March? Well, let’s dive into the numbers and see.

The main thing that I’m happy about is the sodium has dropped finally to a somewhat acceptable level of 72ppm. If I recall correctly, most plants are okay with a level of 40-80ppm of Na. However, I think lettuces prefer a level much lower. We’re on our way. I have deliberately taken my time to reduce the sodium level because I believe a large water exchange would dilute the micronutrients. Now that I’m measuring the micros, I may have to give this fear a good testing to see if it is true. I know that adding pure rain water will dilute the entire system. However, I kind of wonder if the micros can recover faster than I think?

Speaking of micronutrients, I added them to the testing in April. Looks like I will need to look into ways of adding zinc and molybdenum to the system. They keep coming up as zeroes when I run the photometer, although it could be the instrument. Copper is also another one that might need to be added. I got a couple of readings, but lately, the photometer is not picking up any copper in the system.

Lanky lettuce

One thing I’ve noticed is that when the potassium level drops, the lettuce grows kind of lanky and you can see in the photo how there is way too much internode space for a lettuce plant.

They look like solid heads until you peel back the outer leaves.

When I add the potassium bicarbonate to the system, this seems to rectify itself. I believe that due to the sodium dropping and my ability to monitor the other cations, I’m getting a

better head of lettuce that you would find at a

Nice full head of lettuce

farmers market. That lanky lettuce is not salable.

I’ve included my additions to the system for reference. The system volume is about 4000 gallons.

Additions:

Iron: 160g each time on 5/17/16, 7/1/16.

Potassium bicarbonate: 225g each time on 4/26/16, 5/17/16, and 6/29/16.

Calcium carbonate: 370g on 5/17/16, 580g on 6/20/16

As always, let me know your thoughts, comments, or questions by emailing me at doug@tomkatranch.org.