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The Component Ratio is an attempt to quantify growing system volume as a proportion of fish tank volume…..and it’s another one of those silly “guidelines” which purport to guide people while actually misleading them.

One of the more common prescriptions is 2:1……two litres of grow bed volume for every litre of fish tank volume.  

In practice, the quantity of plants that any system can support is determined by its capacity to produce the nitrates that will sustain the plants.

Nitrate levels will be proportionate to the amount of fish biomass that the system contains at any time – and the rate at which they are being fed.  Fingerlings, for example, won’t generate the same amount of nutrient as harvest-ready fish.   As the weather cools, the metabolism of the fish slows, the feeding rate gets reduced and the nitrate production falls.

In reality, the component ratio is only really useful where nutrient levels are able to be maintained at a consistent level…..and this means a system which comprises several fish tanks.  

Some tanks will be stocked with fingerlings and others will be stocked with fish at varying stages of growth up to harvest size.  The University of Virgin Islands aquaponics unit uses four fish tanks for this very reason.

Once you know what nutrient levels the aquaculture side of your system is able to consistently produce, you can calculate the growing space.

Now, many backyard aquaponicists only want (or need) one fish tank.  They usually deal with low nitrate levels by adding packaged nutrients…..like Seasol.  At this stage, their systems are more hydroponic than aquaponic in nature.

To summarise…….without some means of ensuring consistent nutrient levels, talk about component ratios is a waste of time.

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