In this blog I will try to tie together many of the thoughts that have been flying around on my blogs and discussions that followed. I will start by revisiting some important issues that influence my thoughts around aquaponic design, followed by the presentation of arguments in favour of experimenting with component ratios. There has been much talk around these matters. My frustrated thought at one point was something down the line of “I understand that there is a need to have some basic guidelines for people when they start up in aquaponics, but then give them some safe beginning set-up PLUS all the reasons for having the ratios to begin with.” Then the post of Dr Lennard’s calculator came along, and the comments that I saw about it made a very big light go on in my head. I think there are at least two ways people set about trying to rationalize ratios, and if you are from a different mindset, the other ways of doing things appear to be, well, WRONG. If you come from an aquaculture background and spent some time looking at the evolution of AP systems, in particular UVI, you may consider an aquaponic system to be an aquaculture filtration set-up allowing macrophytes in where you may have had to start employing denitrification stages. If you got your grounding in horticulture / hydroponics and you look at some home kits on the market now, they look very much like a hydroponic set-up with fish tossed into the nutrient reservoir. My belief is that it is possible then to say that people in aquaponics either think like a aquaculturalist or a hydroponist.
I am an aquaculturalist. When I see fish and a filter, I think oxygen supply, water flow rates, filter type, media type and surface area required. I think feeding rates and fish food composition. That is why I have an immediate affinity to how UVI and Dr Lennard’s component ratio calculations are explained. Not because I think that these are the only ones that can work, but because I think like these guys do. If you allow yourself to think like an aquaculture person first, and only let the horticulture thoughts peek through once the water hits the plants, you will look at the water movement through filter stages (media or otherwise) and aeration processes in your set-up from the following perspective:
1) How much nutrients have been added into the system.
2) How much metobolites will this result in the water column, and how much sludge can you expect
3) What is the oxygen demand of your fish, and what will the oxygen demand be of the biological agents responsible for nitrification.
4) What type of media am I using.
If you do not address these questions logically, your system design will stumble at the fish tank stage, regardless of how happy the plants may appear. Can you see how these issues above also form the basis of the spreadsheet from Dr Lennard? Your thought process starts at the type of food you opt for, especially in terms of the protein content. Your feed input should be scaled to fish demand – again from aquaculture ratios – and the feed application should be done is such a way as to prevent wastage. Ideally you want to deal with metabolites and excrement only, not uneaten food. You could argue at this point that this line of thought is the same as going for a fish to grow bed ratio. This would have worked for my desire for detail if it was not for the fact that through variable water flow rates and different types of media, you could support vastly different numbers of fish with the same tank and grow bed. This may or may not be an “advanced” issue, but in terms of system components, I believe that people should know where they can stretch their system to one day. Nothing is as irritating to me as realizing that what I have got cannot be expanded on modularly, but have to be replaced.
Having only one set of ratios to go by in the end is an incorrect assumption. That, plus you never knew why you stuck to those ratios to begin with. In my mind, there are no one set of ratios, but rather some important operational targets. These are:
THAT IS ALL. Component ratios are based on equipment used, surface area of media, fish stocking rates, food type, and water flow rates to mention but a few. The correct ratio flows around in a three dimensional space and is influenced by your decisions at critical design stages. It is far better to understand these choices than to memorise something somebody said somewhere. Now, in order for people starting out in aquaponics, some people have become fixated on finding rules and ratios without having the foggiest notion of why these ratios are applied. That helps nobody. That is like the church preaching in Latin to a bunch of illiterate peasants. To go back to an engineering comparison: You have a 1 ton vehicle that you must propel forward at 120 km/h. You have so many choices here that which engine you pick in the end does not matter. 1000 cc, V8, Rotary, Diesel, in the end, the question was not about efficiency or cost, but simply to reach 120. People will get all emotional about their choice of engine, but if they do not acknowledge that their opinion is based on personal preference and that there are multiple possible options, that person is being closed minded. Now that we have the basics out of the way, we can look at ease of operation and efficiencies, about emissions and lifespan reliability, but still, there are more than one way………………….
The following points will lead us there: