One Pump to Many Beds?

[maranatha]

Trying to design system: With a 1000 gal. fish tank and a 275 gal IBC tote for sump tank, is there a way to flood 7 media beds (total 168 cu. ft.) all at one time using an in-line 0.75 hp Jacuzzi pump? If not, is there a way to use one pump and flood 3 separate sections at different times?

[Oliver]

168 cubic feet x 7.48 gallons/cubic foot = 1,257 Gallons. At 50% media displacement that = 628 gallons of maximum water in grow beds, less if not full.

Ideally, you would want to turn over your fish tank water once an hour, depending on stocking density. That is based on 3 gallons per pound of fish, which is high for the type of system you have described. You should limit it to no more than one pound of fish for every 6 gallons of water, or one pound of fish for every 6 gallons of wetted media in your grow beds, and that is a maximum.

If you are flooding and draining your grow beds 4 times an hour then you will need a pump that supplies about 2,400 gallons per hour. Twice an hour would then be half that. I would go with 4 x an hour, or close to it as that will give good aeration to the media (bacteria) and plant roots. Always remember to oversize your pump and throttle back your grow beds to get the desired fill time.

The type of pump you described is probably not the best for this application, as you need good flow and relatively low pressure.

The best way is to rotate sequentially the flooding and draining of the grow beds. You are doing this timing to keep all of the grow beds from all draining at once, overflowing the sump tank and to keep a near steady flow coming from your pump.

You can do this by using a mechanical sequential timer that alternates output to different ports, each connected to a different grow bed, every time the inlet water is turned off and on again; but that requires either a single electric valve to stop and start the water flow into the sequential timer or you can stop and start the pump to cause the sequencer to advance to the next port. Both of those ways require a recycle timer that you set the on and off times and then it repeats. The electric control valve is lifetime rated for a given number of cycles, and we have used them here but they will eventually fail due to the high number of cycles required. Turning the pump off and on will severely shorten the pump's life.

Another way, and the one we use, is to place an electric valve on each grow bed. This means that each valve is only cycling when its attached grow bed needs to be flooded and drained and it extends the valve life over the single valve - sequential timer method above. You can use a separate recycle timer on each grow bed set at the same on and off times for each timer. You then start each timer as the previous one is ending its fill cycle and so forth down the line. They will eventually drift in time and will need to be restarted to keep them in sync. The total on time of all the timers must equal the individual timer's full cycle time, so the last timer in the sequence is finishing its fill as the first timer is beginning its fill.

You can also use a timing controller to operate the individual grow bed valves. We set the fill time of each grow bed to the point that it starts to siphon, plus a few seconds, then turn off the valve and command the next valve to open (as above). We then total all the on times of the individual grow beds and set that as our full system cycle time on the computer, so it all starts over again after the valve on the last grow bed turns off. We use Phidgets controllers that connect to a computer via USB and run software that talks to the controller. As we run Mac computers we use Indigo software, which has a friendly interface and is easy to set up. We are currently using a dedicated older Mac Mini and Indigo accessing lots of different measuring and control systems, including controlling the temperature in our aging spa, which has an older mechanical thermostat (now bypassed) that didn't keep the temperature very stable.

This whole subject brings up the economics of running a system that is larger than a simple backyard system I talk about in Aquaponics 101 (tab at top of the page) and smaller than a full sized farm system, where the control system costs about the same as the in-between system we call a micro-farm, both of which require one computer and software and as many controllers as required.

Oliver

[Oliver]

I just updated the previous post.

Oliver