In Sylvia Bernstein's excellent book "Aquaponic Gardening" she lists four example systems:
In my research of how to design the system, I've seen systems where the the sump pump delivers water to the media beds and these beds dump water into the fish tank via a siphon. The fish tank then overflows the water back into the sump tank. This is the reverse flow of #2.
Since her book has been quite helpful, I wonder why she left out this system? (Sylvia, if you read this, this question is probably just the perverse result of my focusing on the silence :-) ). And yet, this "reverse flow" is how Barrelponics works, just not done with the barrels.
In any case, I would like to know the pros and cons of a system which flows the water from sump, to grow beds to fish, especially in comparison to #2 mentioned above?
Thanks again to Sylvia. BTW: You've started many conversations between my wife and I. :-)
Just a quick reply on this as others will be along for input. On my 650 gallon CHOP if I did it in reverse as you described then all the solids would end up in the sump and cause the pump to clog and need cleaning more often. By draining directly to the media bed I can remove the solids with more efficiency and keep my sump tank clean.
I'm not sure why someone would drain to a sump then to media beds then back to tank. That thinking seems backwards to me for some reason....
David is right the main reason to have the fish tank water flow through the media beds before the water goes to the sump is so that the water being pumped is cleaner. Pump stays cleaner and by not blending up the solids through the pump, you tend to get less suspended solids. With a clean water sump in this fashion you can also pump to raft beds, NFT pipes or towers without as much worry about solids being a problem in those alternative growing methods.
However, reasons people might have the fish tank drain to sump then pump to grow beds that drain to fish tank could be just because their layout doesn't allow for anything else.
Barrel ponics doesn't have a sump so I'm not sure how the comparison works there, it pumps from the fish tank up to a bed in the top which drains to the "flush tank or header tank" which drains to the grow beds.
A sump tank is a low point in a system where a pump has to go.
Now there is another kind of system that is a bit more like what you are talking about. CHOP Mark 2. It is a Constant Height One Pump but the difference is the one pump lifts water to both the grow beds and the fish tank all at once and everything drains back to the sump tank. This design allows for a bit more flexibility in system component heights and these designs do work, however the water in the sump is getting direct fish waste so one would need to add additional filtration to the pump flow in order to feed things like raft beds and NFT troughs since it isn't a "clean water sump."
For a media bed constant height in fish tank set up, I would normally prefer the #2 CHIFT PIST or CHOP design. However it does introduce some major height and design layout constraints. Like you need to have the fish tank high enough to drain to the grow beds or you need to have the grow beds low enough to get the flow from the fish tank. When you switch to CHOP 2 you get far more flexibility with only the drawbacks being that your sump tank may act a bit like a settling tank and require some extra cleaning and you need a larger pump to feed enough flow to everything at once instead of haveing a cascade effect going on from fish tank through grow beds.
My Zipgrow tower systems are essentially CHOP 2 systems in that the pump is feeding the fish tank and the towers and the towers and fish tank are draining back into the troughs/sump tank where the pump is. Otherwise I would have to hang the towers above the fish tank or have the fish tank 8 feet in the air and neither of those are really easy options.
The advantage of a sump is not draining your fish tank when something goes wrong---and something always goes wrong. However, with a system of any size, it's difficult to actually get gravity flow back into the fish tank. Mine goes back into the trough (the sump) which has sides two feet high. The pump in the sump then has a divided output, half goes to a spray bar in the fish tank for aeration. The rest goes to an indexing valve for distribution to the beds.
If the fish tank and the sump were at the same water level, you couldn't get much gravity flow to the sump from the fish tank.
I have the problem of four 4x8 grow beds end to end in a narrow greenhouse. Gravity flow from the furthest two was nearly impossible, so I drain them into a secondary sump with a second pump and a float switch. These are pumped 100% back into the fish tank.
We're using the CHOP 2 and it's been a dream. The sump is pumped to the grow beds, but the beds drain back into the sump, not the fish tank.
The tank receives water from the sump as well, and it overflows back into the sump. The overflow, pulling from the bottom of the fish tank, keeps the fish tank very clean, and the pump keeps the sump clean as well.
The only solids issue so far is with a raft bed which has some solid build up that comes from the sump, which would be expected. We could use a filter, but it's not a lot of build up, and a little siphon hose once in a while will suffice.
Thank you very much, everyone.
The problem of the pump getting clogged I had dismissed since the Basic Flood and Drain dumps the solids into the sump to be pumped. Also, in Barrelponics and even in a two pump system, the pump has to deal with the solids. I just assumed the pumps would handle it. For CHOP 2, does the pump "just handle it"? Can you hear it laboring if/when it's a problem? Hmmm...that's probably a bit too late. Does the "cleaning out the pipes" activity manage the issue just fine so it's rarely a problem?
Clogging will depend on the pump and the screens or grates leading to them. Definitely remove any sponge filters since those are known to clog quickly. If the screen or grate over the pump is too small it can slime up or clog more quickly. In my old big system the pump is an inline pump with a trap basket. When I had it pumping from a fish tank, that trap basket could slime up enough to reduce the flow to the point of siphons not balancing properly and even water quality problems. It is even possible to have a submerged pump overheat from essentially running dry internally from clogging not letting enough water into the pump. This damages pumps.
Now most pumps can actually handle the solids from fish waste and fish food no problem, it is really a matter of making sure the pump screens are appropriately sized not to clog up all the time and you keep all the other more solid debris out of the tank (leaves, sticks, etc.)
I'm one of those people that doesn't believe in the 1 turnover per hour rule of thumb because it's just to expensive and I've yet to see the data stating that my filter can convert all that ammonia to nitrates in one hour. The reason for this is because I have to pay for the power to run the system and it's also designed with solar power and offgrid in the event, god forbid, that we lose all local and state utilities. Also water here is very expensive. Well the water is cheap but they charge out the yingyang for sewer. So their belief is because I am using 1000+ gallons per month then I must be putting it all back down the toilet. Yet there are no exceptions for small farmers. I digress.
My point being is that I have to use smaller pumps and cannot afford to have one "go bad" because I forgot to clean it. I don't believe in a swirl filter because I think those nutrients provide additional benefit once composted by the worms. So I don't employ a swirl filter/settling tank in my setup any longer. The choice is really up to you on how you want to build your own system. I found CHOP to be more simple and less stressful on my animules.
TC is right in that the grow beds are lower but I don't mind so much. They are about 20" high on concrete blocks and that is perfectly fine for me compared to the flood and drain beds that have plants so tall that I need a ladder to reach the fruits.