How Nutrient And Ammonia Levels Interact

Even though they never vary more than a few parts per million, we still test measurable nutrient levels in our systems. At least once a month! The people who taught us in 2007 use highly caustic chemical pH adjusters in their systems to adjust pH swings (calcium hydroxide and potassium hydroxide, neither of which is organically certifiable). We feel these caustic chemicals artificially manipulate these systems into extreme measurable swings of nitrates, but don’t actually provide more usable nutrients for the plants. We used these chemicals for the first few months until we went organic and started using an organically approved buffer chemical, calcium carbonate (coral beach sand). This is why we are so familiar with both these methods of adjusting pH.

(Below) Nitrite/Nitrate test strips (pink, to the left) and ammonia test strips on the right.

During the few months we used the caustic chemicals, we experienced the same pH swings the university documents in their literature, and had to adjust pH as often as every three weeks or so. When we switched over to organic buffering with calcium carbonate, we noticed that we only needed to adjust pH every four to six months; and that pH was rock-steady for months or even years at a time. We also noticed that the nitrate levels in the systems no longer had huge unexplained nervous swings, but were rock-steady at 1-3 ppm year-round, with an occasional HUGE jump to 10 ppm.

The hydroponics guys hate these numbers and tell us we’re lying; even the aquaponics “consultants” claim that 60 ppm is the minimum desired level for nitrates in aquaponics systems. Unfortunately, none of them can demonstrate a way to dependably and accurately adjust nutrient levels in their aquaponic systems.

This is because measurable nutrient levels in an aquaponics system are the result of a complex arrangement that I don’t believe they understand yet, let alone understand how to manipulate. We’ve been organically certified for six years and are just beginning to have a handle on it. We believe what was happening in the university systems when they adjusted pH with these highly caustic chemicals (hydroxides), was that each time they added them, they killed off the majority of their nitrifiers. What happened then is that they would get a nitrite spike when the nitrifiers reestablished, along with a nitrate spike, which accounts for the major swings in nitrate levels these systems experience.

The main reason for this conclusion is that even in our organic systems, with no hydroxides present, we still see these swings. But they only happen once in the operating life of an organic aquaponic system, and that is at system startup. At system startup we will typically see a nitrite spike of up to 10 ppm for as long as two weeks or so, accompanied by nitrate levels of up to 40-160 ppm, lasting from two to six weeks after the nitrite spike is over. After this initial period of high nitrate levels, the system nitrates decrease to the previously mentioned 1-3 ppm and occasional 10 ppm, never varying out of this range in years of operation.

We are the only ones we’re aware of who have operated both the original university-type systems using the caustic pH adjusters, and our organic aquaponic systems using calcium carbonate as a pH buffer. These phenomena we’ve experienced have been in our water temperature range of 68-78° F. We don’t have first-hand experience of this phenomenon in warmer water or colder water. We suspect you might have a higher range of nitrates in warmer water, and a lower range in colder water.

Nitrate Levels:

There is a lot of nonsense out there about “nitrate levels”, and what’s “necessary for aquaponics”. Many aquaponics “consultants” and others claim that 60 ppm is the minimum desired level for nitrates in aquaponics systems. In contradiction of their claims is the fact that none of them can demonstrate how to dependably or accurately adjust nitrate levels in their aquaponic systems.

That’s because they can’t adjust nitrate levels. We’ve operated our systems for seven years now, and the “recommended method” of feeding more fish food just doesn’t create more nitrates (even in our original university systems).

The whole discussion about what level of nitrates is necessary seems silly to us, because we’ve successfully run systems with measurable nitrate levels of zero for months, experiencing explosive vegetable growth the whole time. Please see Add Fish in the Startup Section for more information on how much fish you need, and the fact that it’s almost impossible to have a nitrogen (nitrate) deficiency outside of your startup period. What’s actually happening in your system makes total sense compared to this nonsense discussion.

What’s actually happening: in a mature aquaponics system, you have a certain amount of area that your nitrifying bacteria can colonize, consisting of the roots of all the plants, plus any flat areas in the system such as sides and bottoms of fish tanks, undersides of rafts and sides of troughs. Can we agree on that? Good!

Even though there are zillions of bacteria, and they’ve occupied all the possible surfaces in your system, there are still only a certain number of them; and their population is a number we can at least approximate limits for. Can we agree on that? OK, then it follows that a limited number of bacteria do not have an unlimited ability to process ammonia into nitrites and then into nitrates. Here’s how this plays out in your organic aquaponics system:

We’ll begin with a normally operating organic aquaponics system that we use calcium carbonate in for adjusting pH. In such a system, your ammonia and nitrite levels will vary from 0.25 to 1 ppm; and your nitrate level will vary from 1 to 10 ppm (with occasional periods lasting months in which nitrates are not measurable at all, but the vegetables just keep growing explosively!). As your fish get bigger, it’s tempting to feed them more, so you do. What you will notice at some point is that, as a result of feeding your fish more, and them generating more fish poop, your system ammonia level will begin rising (from its normal range of 0.25 to 1 ppm) up to 2 ppm, then 3 ppm, and so on.

This is happening because your limited number of bacteria do not have an unlimited ability to process ammonia into nitrites and then into nitrates! When more ammonia shows up in the system than they can metabolize and convert, you have simply overwhelmed the ability of your bacteria to process ammonia and the ammonia level will continue to rise until you do something to stop it, such as feeding your fish less.

Although your system will work fine with a very small amount of fish, if you have too many fish and/or feed them too much, your ammonia level will rise. Fortunately, there’s a simple solution to this problem: stop feeding them so much! You can easily go from feeding your fish three times a day to once. If that doesn’t do it, feed them once every other day. After a week to two of feeding the fish less, you will notice the ammonia level coming down from 3 ppm to 2, then to 1, which is where it should be.

The amount you feed the fish controls your ammonia level. This is totally logical: more fish food in, more fish poop and ammonia out, regardless of the number of fish involved. They may get irritated if fed less, but it won’t kill them; fish are not like people in this respect. We’ve omitted feeding our tilapia for up to a three weeks at a time with no ill effects except they splash like crazy and soak the “feeder person” when they finally are fed!

When the situation becomes too extreme, as when you are feeding your fish every third day, but the ammonia level is still rising, you need to sell some fish. Sell half of them and get them out of your system! Although you can’t grow fish at a profit (you lose money, remember?), your fish will still get bigger and bigger until you have too many pounds of fish and too much ammonia. This is the indicator that it’s time to sell fish; this creates cash flow too! Selling fish will help pay for the expense of raising them to be your “fertilizer generator”.

There is one more thing you should know: overfeeding the fish is not the only way to clobber your system with too much ammonia. If you have any other source of decaying organic material in your system, it will give off ammonia as part of the decay process. If your ammonia is rising quickly, look for dead stuff, such as a dead fish caught in a pipe, or a huge mass of roots or other vegetable material that a careless employee dumped into a trough instead of removing (see photo next).