Monday, September 12, 2011

Lessons in Water Chemistry

The Problem:

I think I mentioned last week that nitrate levels were high.  Well, after not feeding the fish for a week, they are still way too darn high!

High nitrate levels won't harm fish right away, but over an extended period of time, they can be dangerous and even fatal to fish.  How high they have to be and for how long in order to kill fish, I have no idea (and it probably depends on the fish species), but with the nitrate level almost off the scale, I felt the need to do something about it.  As a result, we stopped feeding the fish 6 days ago. Amazingly enough, after 6 days of zero fish food, nitrate levels are still through the roof!

Water Chemistry in Aquaponics Systems
For those new to or just getting started with aquaponics, now may be a good time to review just what is going on in an aquaponics system, on a basic chemical level.  There is no need to review any formulas or know any formulas, but you should understand the basic process and what makes it work, and specifically, the following:
  1. Fish excrete ammonia in their waste and through their gills
  2. One type of bacteria converts amonnia into nitrite
  3. Another type of bacteria converts nitrite into nitrate
  4. Both these bacteria are ubiquitous in the environment.  They will naturally come to flourish as long as ammonia is present (no need to add them to an AP system)
  5. Nitrate is plant food and is consumed by plants in aquaponics systems.  This step completes the process of removing what would otherwise be toxic ammonia produced by fish from the water in a way that is beneficial to other organisms - plants, all while recycling the same water in the system.  One way to look at it is, fish produce plant food, and plants produce clean fish water.
In a balanced aquaponics system, ammonia, nitrite, and nitrate levels should be low.  This is because ammonia is quickly converted into nitrate and nitrate is consumed by the plants. 

Stop Feeding Fish - The First Solution to Almost All AP System Problems!

High nitrate levels generally mean not enough plants are present in the system.  I've added plants to my system, but it will be some time before those plants get large enough to consume the quantity of nitrate I suspect needs to be consumed in order for nitrate levels to come down. 

In addition to adding plants, and because nitrate levels were so high, I also stopped feeding the fish entirely.  For anyone worried about fish not eating, thinking they'll starve or something like that, I highly recommend this video by biologist and aquaponics expert Dr. Wilson Lennard.  Skip to about the 2 minute mark for his remarks on feeding fish and you'll see why it's the least of my worries.

By not feeding the fish, the system (through the plants) must consume all available nitrate at the same time that no new nitrate is produced.  That is what should happen.  That is why I am surprised that nitrate levels are still as high as they are (160 ppm - no change from last week).

Theories, Conclusions and Squirly Friends

My current (and only) theory as to why this could be is that inside my gravel grow beds, there are significant amounts of fish waste, and plant roots and other plant debris, from the 10 months or so that the system has been active.  All of that material is continuously decomposing via much of the same processes involved in the convertion of ammonia into nitrate.  Certainly, the fish waste that accumulates in there follows the same process, and other organic waste (such as plants roots) eventually also break down into something that enters the nitrogen cycle and also winds up as nitrate, eventually. 

One factor that could influence all this is the presence of red composting worms added in May of this year and later in June.  The reason these could be having an influence is because after their addition, all that accumulated waste should break down more quickly.  That of course is my assumption and I have no way of proving it.  On the other hand, composting worms are used the world over precisely because they accelerate the composting of organic waste, so it would be pretty silly to think otherwise.

So basically, what I am imagining is that although there is no longer any food being added to the system, nitrate is still being produced via the same nitrogen cycle pathway but using accumulated waste still in the gravel beds instead of "fresh" ammonia produced by fish.  I suspect red composting worms may be playing a large role in the process.

Speaking of our worm friends, here is one of the ones we found today after we dug out the strawberry plants.  They were definietly NOT this big when we added them, so yes, they must be eating something, and they must like it!

Another theory I had, but which I dicarded today, was that worm leachate added over the past week was somehow spiking nitrate levels.
Let me back up first:  besides the worms present in my gravel grow beds, I also have a worm "farm" set up in some plastic bins.  This is NOT a part of my AP system.  It is just a red composting worm farm where I compost vegetable waste.  My system consists of two bins - a lower bin and an upper bin.  The upper bin is where all the food waste goes, and is where the worms are.  The bottom of that bin has some holes drilled into it so liquid can drain into the lower bin.  If you are interested in setting up something like this, I highly recommend this red worm composting site, which is where I got started. 

Being new to red worm composting and not really understanding what is meant by "worm tea", I thought that the liquid which falls into the bottom bin is what is meant by "worm tea".  It turns out this is not worm tea - it is considerd "leachate" and is not recommended for adding to plants except in very diluted quantities.

I did not know this of course, until today, when I finally discovered what worm tea really is.

Before discovering this, I added 500 ml of worm leachate over the course of the last week.  Today, I measured nitrate, nitrite, and ammonia levels in the leachate.  As you'll see in the video, nitrate and nitrite were not detectable, but ammonia levels were very high (50-100ppm).  Obviously, this ammonia would quickly be converted into nitrate upon entering a system where the bacteria necessary for the conversion, like an AP system, are readilly present.  However, the amounts of ammonia added (500 milliliters of leachate), compared to the total volume of my system (4,200 liters), simply do not explain the level of nitrate seen. 

To summarize, the only conclusion I am left with is that some source of ammonia is being converted into nitrate in my AP system.  Since the fish are not being fed, the only source of ammonia present must be accumulated waste from 10 months of running the system.  Since worms were only added after 7 months of running the system, there could very well be lots of waste and tied-up nutrients in the gravel beds that is now currently being released.

The good news in all of this is that it could mean that these systems are possible to run using less feed than is commonly used, especially compared to systems where almost all of the non-soluble fish waste is removed via filters, and in cases where the emphasis is on plant production, not fish production.

My system has two filters - a clarifier, and a "pad" filter.  However, the material that accumulates in the clarifier filter is NOT discarded.  It is dumped into one of the gravel grow beds so it can be decomposed by worms.  The reason it is taken out by the clarifier filter only to be dumped back in the system is so that it does not accumulate in the sump.  Once it is in the gravel beds, which are essentially giant filters themselves, I have little worries about it re-entering the system without decomposing and dissolving first.  The material that is caught by the "pad" filter is thrown away, but only because there is no easy way we have found to get it off the filter pads and into the gravel grow beds very easilly. Otherwise, I'd recycle that, too.  The "pad" filter only filters the portion of water that enters the floating raft portion of the set up.

I have noticed some people with AP systems try much too hard to keep everything clean and filter the heck out of their water.  This is especially true of people with hydroponics backgrounds.  The nice thing about aquaponics is that you can get pretty damn messy and not worry so much about keeping things "clean".  "Dirty", in a biological system/environment to me means something that cannot be eaten (builds up as waste which can become toxic) or that causes desease.  In an aquaponics system, it turns out, almost everything can be and is eaten!  As for desease-causing organisms, of course desease can occur in these systems, but it is much less likely to break out because there are so many natural antagonists present in the form of competeing organisms. 

Below is the video version of most of what's above.  It is waaay longer than I expected/planned, so my apologies.  The point of these blogs posts and videos isn't solely to drive you into a comma! ;)

They are also for me to keep track of what I am doing and thinking, and they are fun to do.  Thanks for reading/watching.


  1. Hey Farmer Brown! Long time no talk...

    Just curious to know what kind of fish do you use? And do you do Aquaponics consulting :).

    Juan Urbina

  2. Juan, I use Tilapia - they are well suited for Costa Rica. I would eventually like to feed them something other than Tilapia feed, which is corn-based, but for now, that's what I use. Corn fed Tilapia have high levels of omega-6 fatty acids, because that is the most efficient thing they can metabolize corn into. That is not the good kind of fatty acid - those would be omega 3-fatty acids. Anyway, those are the fish I use. They are hearty, resilient to highly flexible water environments, and taste pretty good. You just need to be aware that they are not as healthy as other fish might be. I use them as plant fertilizer producers anyway, not so much for eating them, though I do sometimes.

    If you're interested in AP, I'd be more than happy to help you out. It's a lot of fun, and most of the info is already out there!

    PS: Love the icon - that is perfect!

  3. Thanks Patrick! We have a little "estanque" that we've been trying to set up with fish and this might be the excuse to do it. I'm going to look into this AP stuff and I'll let you know.