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250 gal fish tank
SLO to one media filled 3x8x1 growbed with
bell siphon to one 3x8x1 raft growbed with
bell siphon to sump and back to tank. This
setup will be inside with a light for growbeds.
Fish tank will be elevated to overflow.
I have no parts yet. Plan to get a used IBC for fish
and build growbed boxes and use liner. Water
from nearby lake ( maybe fish too).

media bed would flood and drain 2 times to fill raft bed? does that matter?

will the 24 cu ft media bed be enough filtration?

sump minimum size 160 gal?

thanks!

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Sounds good, Tara. I would mention a couple of things that aren't obvious to a newbie.

First, I am repeatedly amazed how slowly water flows trough media, even fresh media with no roots and sludge. To fill an 8' bed from one end, it will start siphoning at the other end and often drain and break the siphon without ever draining the entry end. To combat this, use several drain points tied to one external bell siphon.

Second, having one bed siphon to the next siphon bed may result in this: suppose the first drains to the second and breaks, the second, however did not fill enough to begin siphoning, so it remains nearly full. Now when the first fills and drains again, it will no doubt start the second draining, but will now be filling the second perhaps faster than the second can drain, resulting in possible overflow, or at least wet media, which is to be avoided (fungus and fungus gnats). Beter would be to split the SLO to simultaneously fill both beds, and each bed drain independently and directly to sump.

Third, SLO drains work great. But make them easily removable for cleaning, and oversized. Gravity doesn't push water through a pipe like a pump does. I have a 1 1/2" pvc SLO affixed to a 120 gal tank, and it will BARELY keep up with 120 gph pump rate. If any sludge or biofilm reduced the flow, my FT overlows. Personally, for a 250 gal FT, I would use a 3" SLO.

if this was my setup i'd have a few smaller grow beeds so their would be more siphons to keep the out flow of h2o constant an have the out flow drop to the sump, from the sump pump up to the raft bed and have the raft bed use just a stand pipe  instead of using a bell siphon, and have the rafts system directly flow to the fish tank.

i hope you can make out what i am trying to say!

I don't see why you would empty the raft bed with a siphon. Makes more sense to just let the water run out constantly through an overflow.

Sounds reasonable otherwise.

Be aware that you don't absolutely have to have an auto-siphon in the media growbed either. I'm liking constant flooding more and more, as auto-siphons don't always work and it sucks to discover that your growbed hasn't been filled for a day or two.

Thanks Jon,

I had not thought about water moving slowly thru the media. I am thinking of using 1/2-3/4 inch river rock. Water would be much slower to move thru that than simply drain from a tank!

Also I am rethinking the fills. I had planned to use a 3' SLO. It was suggested probably for the same reasons as you.did.

More simple is better and to fill both at the same time means they can be at the same level so, better for the light placement.

About the SLO being easily removed...pvc joints need not be glued right? They have no pressure to leak?

Thanks again.....any thoughts you have are welcome. I will post with other questions and any progress made.



Jon Parr said:

Sounds good, Tara. I would mention a couple of things that aren't obvious to a newbie.

First, I am repeatedly amazed how slowly water flows trough media, even fresh media with no roots and sludge. To fill an 8' bed from one end, it will start siphoning at the other end and often drain and break the siphon without ever draining the entry end. To combat this, use several drain points tied to one external bell siphon.

Second, having one bed siphon to the next siphon bed may result in this: suppose the first drains to the second and breaks, the second, however did not fill enough to begin siphoning, so it remains nearly full. Now when the first fills and drains again, it will no doubt start the second draining, but will now be filling the second perhaps faster than the second can drain, resulting in possible overflow, or at least wet media, which is to be avoided (fungus and fungus gnats). Beter would be to split the SLO to simultaneously fill both beds, and each bed drain independently and directly to sump.

Third, SLO drains work great. But make them easily removable for cleaning, and oversized. Gravity doesn't push water through a pipe like a pump does. I have a 1 1/2" pvc SLO affixed to a 120 gal tank, and it will BARELY keep up with 120 gph pump rate. If any sludge or biofilm reduced the flow, my FT overlows. Personally, for a 250 gal FT, I would use a 3" SLO.

Thanks for the reply Loki (great name). Am I correct in thinking a stand pipe alone will drain much more slowly than with the "bell" over it?

 I am thinking the beds should both drain into the sump. And probably be filled at the same time.

Would two SLO from the Fish Tank be ok? One for each bed?

I may be planning overly complicated flows here?

loki said:

if this was my setup i'd have a few smaller grow beeds so their would be more siphons to keep the out flow of h2o constant an have the out flow drop to the sump, from the sump pump up to the raft bed and have the raft bed use just a stand pipe  instead of using a bell siphon, and have the rafts system directly flow to the fish tank.

i hope you can make out what i am trying to say!

So the raft bed would always be full?

I was thinking the root system wants some time w/o water at all? As in flood and drain.

Or would that happen in the way you suggest?

Clearly, I need some help!!!

Flemming Funch said:

I don't see why you would empty the raft bed with a siphon. Makes more sense to just let the water run out constantly through an overflow.

Sounds reasonable otherwise.

Be aware that you don't absolutely have to have an auto-siphon in the media growbed either. I'm liking constant flooding more and more, as auto-siphons don't always work and it sucks to discover that your growbed hasn't been filled for a day or two.

Yes, the raft bed would always be full (just a plain stand pipe). A couple of air stones in the raft bed would help growth, and probably help move/mix water along.

Constant flow/constant flood media bed might be a really good option too, because of the reasons Flemming mentioned, as well as there is an argument to be made (as RupertOfOz has made) for a constant flow through the raft being more desirable that the rushes that would come with flood and drain. (Which one would gain by having a constant flood/flow media bed before it).

Hmm, I totally overlooked in the OP that the second bed was raft. So yes, raft stays full and overflows over the standpipe, typically. In an 8' bed you may not need to aerate the raft bed, but it sure is nice if you can, and provides some insurance that plants will remain happy if water flow us interrupted for a while. The whole idea of a flood an drain raft bed has got me thinking, as I have truly never considered it. I think it's a great idea. If the rafts had only minimal room to float, and would rest on ledges as the water began to ebb, then the plants would surely benefit from the air time, and no air pumps would be needed. I'm not big on styrofoam anyway, and rafts can be made from wood or whatever, if not actually resting on the water. Gonna have to play with that idea.

If your 24 cubic foot media bed is only flooded 10", leaving the top 2" dry, then the remaining 20 cubic foot will displace about 60 gallons. If your raft bed remains full, then of course it requires no sump displacement. If you decide to build raft with a siphon, and assuming it fills to 11" and drains completely, then it will displace 165 gallons. And I like to sump at least 20% system volume for evaporation/transpiration. That should help in designing sump volume.

Jon if you had the rafts hung up on ledges it might be enough just to keep a 2" or 3" air space between the top of the water and the bottom of the raft. The trick I guess would be to keep the relative humidity quite high. There's a guy (Dr.) Kratky from Hilo who developed such a method for growing hydroponically quite a whiles back.

This is from... 

Kratky, B.A., 1996, Non-Circulating Hydroponic Methods, DPL Hawaii, Hilo, HI.

Many hydro authors use and/or describe his method in their own works when giving overviews of the different systems/methods widely in use in the hydro world. This seems a bit less risky than totally draining the raft while still garnering the benefits in terms of O2...

Just a thought...

Indeed. And some good air bubbles snapping would no doubt give you the humidity and aeroponics style zone in the diagram. However, flood and drain would too, perhaps even more so, without any added component of air, stones, or pumps. What worries me is power outage while drained would rapidly dry raft roots, and I definitely plan for the worst in these situations. So how about both? A minimal air flow in raft bed, and maybe 2-3" of siphon displacement, from 11" down to 8-9", then back to 11". That would improve mixing and aeration greatly over constant standpipe, with minimal risk when pump fails. Hmmmm?

Yeah, no fears in case of pump failure was the "less risky" part :)

Your idea sure seems like a good one. Certainly it would work. The question would probably then just be 'how much benefit' over doing it the lazy Kratky way..?

But, get this as far as "risky" goes...If it means anything to you, I have some 2-1/2 foot tall basil plants and one of those yellow cayenne peppers growing in a small DWC bin that usually only has like a half inch of water or a bit more in it and 2 air stones spitting air and some water into nothing but air space air, and the plants are doing well. I'm quite surprised. It's like a faux, really fucked up super half assed aero-ponic, low nute sorta deal. I doubt I would ever base a commercial system on such a model, but it's been working just fine for months now. (I should add that the foam seals off the edges at the top of the bin and keeps the moist air trapped...kinda like how I had those dual root-zone and PL-L test bins set up... I doubt it would work otherwise since the air, and then the roots would in all likelihood simply dry out)...But your proposed method would seem to mitigate such risks...

Here is one example of such a design to manage a slightly variable height in a dwc trough. Leaves the air gap for part of the roots and the trickle draining action helps re-mix new air into the high humidity zone.

http://youtu.be/HY6d1n_NfV8?t=5m13s

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