An interesting discovery.

[Chris Smith]

In October Coastview Aquaponics replaced net tanks with a media bed in our commercial system. We used black cinder and composting worms with a loop siphon in the media bed. From the media bed the water goes to 4- 40 foot raft troughs. The media bed has worked great and the worm population has exploded.The health of my raft troughs have improved greatly since adding the bed.

I have had one minor issue of poop building up in the area where the water enters the bed. I call it a minor issue because it is easily solved by moving the dumping point and giving the worms time to catch up.

A few weeks ago I had a pump failure in that system and I did not have a similar sized pump to replace it. I had one pump way too big and several smaller. I first hooked up the bigger pump and it pumped so much water that my siphon(1 1/2 flexible tubing) would not break due to too much water entering the bed. This big pump also flushed excessive solid poop into the gravel.

I then decided to try an experiment partially based on Murrys chop system. I placed two small pumps into my sump and plumbed one discharge into the fish tank and the other to the media bed. The two pumps have a combined output comparable to the original one. The water coming out of the fish tank is now about 1/2 of what it was. This allows the water more time in the FT. This extra time allows the solid waste to break up more in the aeration system for the fish. Since the solid waste breaks up more I don't get the poo pavement problem any more.

The nutrients in the system seem the same as before as well. The water in the FT builds up a little more but nothing out of the normal range. The FT water is combined with the ST water in the media bed and blends. This system seems to be working better than my original system of using one pump.

[TCLynx]

And it provides you some redundancy, as in if the pump going to the fish tank fails, you can switch the other pump to feed the fish tank and have a little time to get a replacement or fix the busted pump before things to too pear shaped.  Might not be enough flow to kick the siphon but letting a bed run constant flood for a few days won't kill it and might even be a good time to germinate seeds in the bed.

 

Thanks for the info, will be interested in how the media bed works out long term.

 

Can you list for us some stats of Fish tank size, Media bed size, raft bed size, flow rates, and aeration rates.  Volume as well as square footage would be helpful.  And perhaps the average feed rate or fish load might be helpful to know.

 

I've found that the fish poo pavement and bio-slime build up tends to be a problem in media beds with constant inflow while my beds that get intermittent inflow don't seem to have the problem at all.

[Kobus Jooste]

Interesting, these accidental discoveries.  If you re-calculate your water flow through your filtration media based on the fact that the water is now of "mixed" origin, how does your water volume throughput through the filter compare to classic recommended ratios?