I gotta say it’s really fun to take these measurements and see how the system performs. Up until getting the photometer, I only had a rough idea of what was truly in our system. The little test strips can tell you whether or not you are screwing up, but they really can’t tell why you are screwing up. Being able to measure and record what is actually happening is extremely informative and empowering.

Here are the results:

I’ve been keeping this spreadsheet along with notes of when we clear the swirl filter and net tank along with additions of water and things like iron or calcium carbonate.

A quick look at the numbers shows a few little things:

Nitrate is at adequate levels for growth and there was a dip in June as we added the third trough to the system.

Nitrite was pretty high in February and I was having some filtration issues at the time. I was chasing my tail for a little while there. We made some changes to the plumbing and it seems to have helped. There was a little spike in June and that’s probably because I usually clear the filter on Fridays and the nutrient analysis is done on Mondays. All the stirring up of solids probably contributed to the spike is my guess.

Phosphorus and Phosphate look to be fairly normal.

Before getting the photometer, one of my biggest concerns was potassium. So many aquaponicists recommend using potassium bicarbonate to increase alkalinity and it works really well to do just that. However, the levels of potassium start to build up over time. Potassium can have antagonistic effects on other nutrients in the system like calcium and magnesium. The plants were getting tip burn on some varieties and I was concerned that maybe we didn’t have enough Calcium. I was pretty sure we had too much K in the system except our alkalinity was dropping, so I kept adding more and more bicarbonate. I started adding calcium carbonate and some calcium hydroxide to adjust the pH and the system stabilized. Shortly after this time, I switched to the well water and now I don’t add anything for alkalinity since the alkalinity of the well water is 300ppm. It will be interesting to see how the system performs this winter when we get more rain water.

Calcium stayed relatively stable. There is a healthy population of ostracods in the system. I consider them to be a time released calcium source as they live in die in the system. Calcium is coming from the winter time calcium carbonate additions, our well water, and our ostracod friends.

Both Magnesium and Sulfate have dropped since February because I had added some magnesium sulfate in January. Why did I add epsom salts? Well, because I thought I needed to add it. The photometer now helps me make these decisions with more information instead of being a “chef” just tossing in ingredients to taste.

Alkalinity has been stable. Lately, I’ve been using well water and the alkalinity is 300mg/l. Over the winter I was using rainwater to try and lower the sodium in the system. That meant I had to add alkalinity in the form of potassium bicarbonate, which raised the potassium to high levels. I was concerned about this and added calcium carbonate and calcium hydroxide to add more alkalinity and raise the pH back up because it was dipping. It worked really well and alkalinity stabilized. I was doing a lot of guesswork as I did not have the photometer yet.

Sodium has always been extremely high. Next winter, I hope to have more rain catchment in place so that we can try and reduce the sodium levels. Things grow pretty well in the system. Some varieties struggle with the excess sodium. I would love to see how the system performs with a normal range of Na instead of hovering around 200mg/l.

Iron is added every few months or so. Last addition was 10 ounces of chelated iron (DPTA) for about 4000 gallons. We want to stay around 2mg/l of Fe.

Ammonia has been fairly normal in the system. Nothing too surprising here. I’d like it to be lower, but it seems fine.

Electroconductivity is within an acceptable range.

pH is hovering around 7, but since we’ve moved back to well water, it is just above 7. I’d like to get it closer to 7 or a little below for more plant nutrient availability.

I’ll continue to publish what we find as the measurements continue…