Backyard Aquaponics
A place to discuss aquaponics

Hi All,

I'm planning on doubling the size of my AP systems and like some advise and or thoughts you guys might have that I haven't thought of.

Generally the idea is to convert the concrete lined in ground trampoline pit and build a meter high wall around the top edge and line the whole surface with a fish safe liner. Add floating raft troughs, tube systems and enclose the whole area with translucent poly carbonate sheeting.

The bottom of the pit has a shallow taper so will need to be made steeper to collect the waste. I intend to pump up into the GBs and drain back in to the FT however because both systems have STs i would need to bypass them and go directly to the FT which will determine the water level height and over all volume.
A thought I had was on fish density, ATM I run 20 10-11" trout (survivors from last summer) in 1 IBC sy2 and are going to get another 30 4" for sy1 which is about 40lt per fish. So the 20KL would hold 500 fish for the same ratio which is too many. How many could I have at a minimum? 100 -200?

I don't think we have enough information. The fish count will depend on the amount of filtration (grow beds, biofilters etc), not just the tank volume. If you're looking to see how many fish you need to drive the nutrients in the system to have enough for the plants that varies with the type of plants.

> How many could I have at a minimum?

The obvious answer is 1

With enough GB media volume planted out you could easily have 500. One year I had over 400 RT in my 9500l FT with 10 GBs and 5 WBs, but I had some losses in hot weather when an air pump failed. Currently I have about 250 in the system, and about 20 of them are left over from last year, some now weighing over 2kg.

Do you notice a growth rate difference in the plants when there are less fish?
And can you recommend an air pump for 2m depth?

Yes, less growth occurs with significantly less fish, but I can't really notice any difference between 400 and 200 for my existing GBs.

Don't put your air in at 2m, half a metre is plenty. This puts less load on the pump diaphragm, causes less internal heating due to compressing the air less, and still provides plenty of aeration. Mine are only about 0.5m depth, but give a good up in the middle and down at the sides circulation, which moves solids towards the centre at the bottom of the tank.

My current pump of choice is the Jebao PA-60, for its low noise level and electrical efficiency.

Thanks Gordon,
I had a look at the pumps they seem well engineered.
What size air stone(s) do you use?

After having another look at the discharge height of the GBs the tank volume will be closer to 16KL.
Do you think insulating the vertical sides of the 5.3 x 3 x 1 m high walls of the above ground section is beneficial?

In summer I can shade the tank area but wonder about whether or not the solar effect on the GB water will exceed the low level ambient temp in the green house. The solar effect on the present IBC FTs reach 27 degrees but I'm thinking with the larger volume and less exposed to ambient, more exposed to ground would result in slower temp changes, lower over all temps and ammonia levels.

I'm using large air discs, I think there are pics in my large system thread near the start.

I have 3 air discs in my large system, with 2 air pumps running continuously, one on a battery powered inverter charged by a PV panel (daytime) / battery charger 25min on per 2 hours at night.

Yes the insulation is beneficial, but you need to make sure the ground around anything buried in the ground is well shaded in summer, as the hot ground slowly heats the water, and it doesn't cool down a lot at night. With the extra water volume, the temperature changes are slower, but also harder to do anything about.
All my GBs are set into the ground, and that is where most of the heat gets into the system.

27C sounds rather hot for trout to survive!

Oh yeah that's when they croack if the temp gets there real slowly but if it moves fast they croak at 26 degrees or a 2 degree spike and they done.