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.
-o0o-
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daily feed rate and food conversion ratio determine what nutrients are left over for the plants. Plant nutrient needs is the other factor: Fruiting plants (tomatos etc…) need more nutrients than i.e. lettuce. Only if you keep this equilibrium as constant as possible you will optimise your system. Temporary peaks in nitrates luckily are not harmful to the fish. Plants like duckweed and watercress somewhere within the loop could help by “moderating” this.
Frank…….while temporary peaks in nitrates are not harmful to fish, they can (at high levels) inhibit fruiting in plants.
The equilibrium to which you refer seems to be a feature of the UVI aquaponics systems…..where nutrient levels are maintained at a constant level by having four fish tanks hooked up to a given quantity of plants of various stages of growth.
Duckweed has long been regarded as a suitable plant for bio-remediation. We usually keep duckweed in our systems because, (according to researchers) not only does it harvest ammonia in its un-ionised (most toxic) form, but it also provides food for the jade perch that we often grow.
We also use the duckweed tank as a sedimentation tank. The water velocity through the tank is such that it allows sedimentary solids to settle out. We remove these solids at the same time that we harvest the duckweed.
May I just say, Gary, THANK YOU for posting all of these helpful “myth-busters” about aquaponics. There is literally too much useless info out there. I am a newbie and am attempting to lower the risk of killing all of my fish and plants right from the start by reading about it endlessly. However, it’s tough to differentiate from the fluff.
Rose……I’m pleased that you found it useful.
Absolutely…
So one needs to know what the nitrifying capacity of their selected grow media as that will limit the fish to plant ratio if they are operating without a bio filter. Those with a filter can simply and accurately know the ratio, if they know the TAN production of the fish volume they want to grow or they know the plant nutrient uptake. Either or, they can deduce one from the other to gain the “magical ratio” for their selected species of plant and fish based on their system design.
If on the other hand we are talking about the “systems” currently toted about by aquaponic suppliers, then your guess is as good as mine.