Newbie converting fish pond???

[Greg]

I’m a total newbie to Aquaponics seeking advice. I have recently been looking for a better filtering system to maintain my rather green small fish pond, (about 280 litres). We also wanted to start a small herb garden – then the Gods sent me Aquaponics. Very logical when you think about it, one of those ‘why didn’t I think of that’ moments.

What I don’t understand is, if the accepted volume ratio of 2:1 i.e. the grow bed is twice the volume of the fish tank is correct, & the amount of water required to fill the grow beds with medium (I’ve tested with blue metal) is half the actual volume of the grow bed, how do you stop the fish tank from emptying or at least dropping significantly. I’m hoping to install a flood type system but I’m obviously overlooking the obvious???? Suggestions welcome.

[DaveOponic]

I use a trickle system rather than flooding the grow bed. The amount of water in the pond isn't affected too much by the water in the system. I also have an NFT system with 3 8 foot pipes connected to my pond. As well as this, I have a 200 litre drum acting as a bio filter. Both of the growbeds are on a timer. the pond probably holds about 1000 litres and when all the water is circulating the drop in water level is maybe two or three inches.

I guess in a smaller system if you want to flood and drain, you could add a drum to act as a sump. Pump the water into the drum first and then flood the growbed.

[Jonathan Dyer]

Hi Greg,

Having around 280L don’t expect much from the system whatsoever a few plants at best will use almost all the nutrients your fish will produce.

As for volume ratios they are not really based on any scientific guidelines its just what people have tried and has given results. Personally I think they are a waste of time in some respect as surface area (m2) is a better representation of what can be physically grown (for the technical side it also ties in with bacteria population), anyway my ratios would be something like 7:1 (7 being the fish tank: 1 being grow bed). Aquaponics is about balance, the more fish you have the more grow bed area you will require to keep up with ammonia loads. When you have ammonia, nitrite readings at Zero and nitrate readings low in your water you don’t have enough fish to allow for proper plant growth and development so you either add more fish if you can or add organic or inorganic fertilisers to fill the gap, but trace elements (especially iron) are needed all the time for proper plant growth so they need to be added on a regular basis.

How to stop the tank from emptying? You have discovered the fundamental flaw with flood & drain that’s why I don’t use it, with a continuous trickle flow system you are keeping the water levels constant, no float switches, no timers it is less of a burden and more reliable, there are one or two other ways (Chift Pist) but = more hassle and more manufacturing = more money. To put it fast and simple a continuous flow system is where water is pumped up to the grow bed, Lengths of PVC is run along the bed with holes drilled at intervals to let the water escape, The water then drains through the bed back into the tank from where it started.

I would say that one 200L drum cut in half would meet much more than the demand your pond would ever produce. But don’t overlook other systems NFT, DWT, Floating Raft and a few others but as far as wanting better filtration for your green pond a blue metal bed would be the wiser choice I think.