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5 Reasons why Aquaponics Filtration Works

With aquaponics filtration, especially biofilters there are a few schools of thought and all are equally good for your plants and fish. To keep things simple, some will want to use a media grow bed in their aquaponics as their primary biofilter and these work perfectly well provided your stocking density or more importantly your fish feed input matches the available surface area of your media.  If not disaster will strike at some point in time as your fish grow. [heading] Why Aquaponics Filtration? [/heading] There are a few downsides to having just the media grow beds as your biofiltration: If you are not removing solid wastes (fish poop and uneaten feed) your growbed is required to have sufficient capacity to oxidize or break these organic wastes down into a form which your plants can use.This is often referred to as mineralization, which is not an accurate assessment of what goes on but it will do because we are familiar with the term.  In short grow beds do not have a great capacity for oxygen required to oxidize. Ammonia is not an ideal nutrient for plants and adding it directly to the grow bed from your fish tank, will work but should your bacteria have a bit of a slack time of it like sudden cold or your beds become very acidic (pH < 6) then the ammonia will accumulate and overwhelm your fish and become phytotoxic (poisonous to your plants) reducing the overall performance. Competition for space and food within the bacterial populations becomes fierce with the inclusion of organic wastes.  Another prominent species of bacteria called Heterotrophs can increase in number rapidly and dominate or basically smother your nitrifying bacteria again reducing the efficiency of your growbed as a bio filter. Low oxygen concentrations within the grow bed can occur.  While this does not present a great issue for your plants or your bacteria provided the oxygen does not drop below 2mg/L (something you are not really going to measure), it will deliver lower oxygen levels back to the fish.  In this case the grow bed becomes a very large oxygen demand on your system. Elevated Nitrite will indicate your bed need cleaning or flushing because it has become overloaded with organics.This happens generally when you have elevated Nitrate and low oxygen (anoxic).  This particular combination in the growing environment completes the nitrogen cycle where the Nitrate becomes the electron donor. In other words the bacteria take oxygen from the nitrate (NO3) for there own growth reducing it to nitrate (NO2 <–see the reduction in O2?) then bacteria take it a step further to nitrogen gas (N) if oxygen levels are sufficiently low.  Often oxygen is not low enough for this to happen so the Nitrite sticks around until your nitrifying bacteria can get to it, which will leave your fish exposed. All of these are very much a chain reaction and can be easily avoided if your fish feed input is not too high.  But what is too high?  Very complex question to answer.  So to simplify this it is often best to put a simple solids filter before your growbed.  Doing this will remove some of the guesswork and finger crossing. On the other hand, my preference is to include a small biofilter precluded by a solids filter before any growbeds of any type, shape or form.  Be they NFT, DWC, Media, Growbags, soil or what every you like.  Quite often I hear questions around why I would add such complexity to my system.  My answer is because the filtration simplifies the management of the system.  They effectively do the management for me and with a little bit of planning it saves me the complexity of managing the water quality. Keep an eye out for the next installment about why I use aquaponics filtration in my system. Regards Paul…

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