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Nitrate Management Without Plants

I'm new to aquaponics and I'm trying to get everything figured out...at least to the point where I have some grasp of the concepts and ideas behind it. My current question deals more with aquaculture rather than aquaponics. In aquaculture, where no plants are being grown, just an aquarium environment, what do we do with the nitrates? After the a new aquarium has completed its cycle, and ammonia and nitrite levels are zero, how do you control nitrates. In the aquaponics systems, the plants consume the nitrates. In a system with no plants, will the nitrate levels rise to an unsafe level for the fish? Or is it even necessary to worry about the nitrate level as long as ammonia and nitrite levels are low or zero? I have heard of doing occasional water changes to aquariums. Is this due to the nitrate level rising? I ask this aquaculture question in the aquaponics forum because I do plan to add plants later, after the fish have found a nice environment and have grown to adequate size. Thanks so much for any info you can give me.

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Permalink Reply by TCLynx on April 19, 2012 at 7:17pm

James,

In aquaculture they change out water just as should be done for unplanted aquariums. Nitrates can rise to an unsafe level for fish. This is the reason that aquaponics is better for the environment, because we are not having to dump and replace the water for the fish nor are we needing to dump and replace nutrient solution for the plants, we just top up.

Now there are some methods of filtration and denitrification that can get rid of some excess nitrates by essentially offgassing them as atmospheric nitrogen gas but that can be a complex discussion though you may find information about in it koi forums. It usually requires an anoxic zone in the system and then a means to really aerate the water to keep from experiencing a nitrite spike instead of letting the nitrogen degass into the air.

Permalink Reply by georgia washington on April 19, 2012 at 10:34pm

Thanks for the reply, TCLynx. You confirmed what I was thinking. I will try to locate a good website that can explain what safe nitrate levels are for tilapia and recommended percentage of water change when the level becomes unsafe. I'm and extremely new to every aspect of aquaponics so I really do appreciate the time you spend helping us beginners. I would like to add that I have ran across your website and have read several of your blogs and have seen the great aquaponics diagrams that have been extremely helpful. Thanks for all the time and effort you put into helping others.

TCLynx said:

James,

In aquaculture they change out water just as should be done for unplanted aquariums. Nitrates can rise to an unsafe level for fish. This is the reason that aquaponics is better for the environment, because we are not having to dump and replace the water for the fish nor are we needing to dump and replace nutrient solution for the plants, we just top up.

Now there are some methods of filtration and denitrification that can get rid of some excess nitrates by essentially offgassing them as atmospheric nitrogen gas but that can be a complex discussion though you may find information about in it koi forums. It usually requires an anoxic zone in the system and then a means to really aerate the water to keep from experiencing a nitrite spike instead of letting the nitrogen degass into the air.

Permalink Reply by TCLynx on April 21, 2012 at 7:38am

You are welcome James.

There are a couple means you could follow and it will depend on how available water change water is to you and how often/much time you are ready to put in.

You could simply use the Freshwater master test kit and do changes to keep the nitrate levels in the orange (readable range) and for stability smaller water changes much more often are usually better for the bio-filter and fish. 10-20% water changes are what diligent aquarium keepers might do weekly.

Or you could look up the info about safe nitrate levels for tilapia and you will probably need to learn to do dilution tests to get the readings using the master test kit or you need to get some other type of test kit that will let you track the nitrate levels in the higher range and that water will really be rich when you do water changes and you will want to have some very greedy plants to water with the change out water.

Now if you have an easy way to grow algae using that rich water to feed your tilapia, it might be handy.