Sometimes we learn more from our systems when they are not exactly operating at their best than when they are running at their peak. It is currently winter over here in South Africa, and for the first time in years, El Nino’s grip has been broken and we are seeing rain and cold fronts aplenty. So much so that I decided to move my aquaculture-sourced tilapia into the larger greenhouse. The mixed system is essentially running fishless, with a dab of ammonia every now and then. It usually have 20 kg’s of hungry fish in it, and the effects of taking them out is clear. With water temperatures seldom above 16°C in the mixed system, the fish would not be feeding at all and thus having moved them seemed to be the right decision to me. The wild fish can take single figure night temperatures but I did not want to risk it with my aquaculture bred colour variations.
Well the passion fruit is still happy, although growing very slowly. I have about 100 fruit maturing and just 10 per month is worth my power use. What got my attention though was the strawberries. I was starting to hate them this summer. I had runners all over the place, but few fruit. I was wondering if I had the wrong type in the system, but then the fish came out and the plants changed their attitude. Almost all of them are flowering now, in the middle of winter. Strangely coincidental, a friend of mine that knew about the summer issue came back to me at the same time with some input from some Dutch face book contacts – too much nutrients results in vegetative growth in stead of fruit. So there. I have always known that my system can still expand in terms of the NFT components I wanted to add, but without adding anything new in the few months of late summer, the nutrient levels never dropped low enough to convince the strawberries to fruit.
This realisation that my small unit can be expanded much further without needing more fish is spurring me on to make as much of the winter servicing and expansion time that I have left before spring arrives. I think about the mixed system design theory that I have been working on, and think I under-estimated the volume of plants that can be sustained in a mixed system. My gravel beds are adequate for mineralization space, and just about enough for ammonification. The Ammonia levels have always been safe, but never below 0.5 mg/L. There was always relatively easily detectable Nitrate levels. What I think I will do this summer is cut back on the fish load just ever so slightly, and add those aeroponic components that I have been contemplating. This should put me back into the sweet spot that the system had when it ran on a third of the fish it had this summer.
All of this does seem to undermine one of my core aims when I started the mixed system path that I am on though. I wanted to reach a point where I had a highly productive system on a small footprint, capable of yielding a lot of fish and vegetables. This was a response to the multitude of enquiries from a development perspective here in South Africa, with people looking for as many “meals” as possible coming from a domestic system. After looking at aquaponic options for a while now, I am becoming more and more convinced that the fish component is going to be shrinking in future systems rather than increasing. I predict “running on fumes” units being far more stable than “running hot” units like the one that I tried to have for over a year now. I am looking forward to testing this notion in the coming months. I’ll be dropping the fish component by around 25% while adding about 60 – 80 NFT pot spots. Lets see how this pans out.