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Ebb and Flow cycle times and the effects on plant growth
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Author:  trippytoads [ Mar 19th, '09, 07:24 ]
Post subject:  Ebb and Flow cycle times and the effects on plant growth

Hi all,

I'm very new to aquaponics and I just got done building my first system. My question is about the flood and drain cycle times. It seems obvious that you can have too long of a cycle time such that the roots of plants dry out. What about too often? Is there a cycle time that is too frequent?

My system currently can cycle every 2-4 minutes with some slight adjustment to the input rate. I just keep the pump on all of the time. I can adjust the rate slightly but if the fill rate is too slow then the 1" drain will be able to empty the water sufficient without creating a siphon. The higher flows will create a siphon but at the cost of having the system cycle often. Is this an issue?

Author:  TCLynx [ Mar 19th, '09, 08:13 ]
Post subject:  Re: Ebb and Flow cycle times and the effects on plant growth

How often is too often will depend on your media and the plants I guess. So long as the roots get enough air, things should be ok. Some media that holds water too well (like sand, coco coir, peat, etc) might just been too wet for many plants flooding and draining that often. As to if your set up is cycling too fast or often, well you might just have to wait and see how the plants do. It does seem pretty fast but who am I to say it won't work. Fastest I've cycled systems is usually between 15 and 30 minutes between the siphon kicking in.

How big is your system? Pump? Growbed? Fish tank?

Author:  tamo42 [ Mar 19th, '09, 09:08 ]
Post subject:  Re: Ebb and Flow cycle times and the effects on plant growth

trippy, I have the exact same situation in a new GB I set up. I put in some seeds, and they're sprouting with no problems. So it might be just fine :D

Author:  trippytoads [ Mar 19th, '09, 09:12 ]
Post subject:  Re: Ebb and Flow cycle times and the effects on plant growth

The system so far is made of what I believe is a 50 gallon grow bed and a 270 Gallon pond. I'm using expanded clay for the grow media.

Like I said I've tried to slow the speed down but the 1" drain won't siphon unless the flow is fairly high. The pump is a 550 Gal/hour pump. I plan on having 3 other grow beds so my thought was to have a fairly beefy pump.

I've added some pictures but I swear that the water is much better now. So right now the system takes two minutes to fill and two minutes to drain. At best I can get it to a 4 or 6 minute fill with a 2 minute drain without adjusting the standpipe of the drain.

Attachments:
File comment: Here is the bell siphon.
Bell_Siphon.jpg
Bell_Siphon.jpg [ 49.56 KiB | Viewed 4169 times ]
File comment: Side view of the whole experiment.
IMG_0757.JPG
IMG_0757.JPG [ 44.71 KiB | Viewed 4170 times ]
File comment: This was taken as I was adding the expanded clay grow medium.
IMG_0767.JPG
IMG_0767.JPG [ 46.47 KiB | Viewed 4169 times ]

Author:  TCLynx [ Mar 19th, '09, 10:29 ]
Post subject:  Re: Ebb and Flow cycle times and the effects on plant growth

Looks like you are probably pumping almost twice the amount of water needed to keep that size tank happy. The good part about this is the pump is big enough for expansion. However, I would suggest that you use smaller siphons for the future beds so you don't have to hear them slurping every few minutes. Also, as you branch the pump out to fill more beds, you might not have enough flow to keep the really large siphon working so downsizing the siphons a little bit might be needed as you expand.

As you said, you can only adjust it so far before the siphon won't kick in properly. Can you cut the flow to 1/2 or 1/3 and still have it work? If not, you should be prepared to change out the siphon when you bring the other beds online.

Good Luck with it.

Author:  Dufflight [ Mar 19th, '09, 15:02 ]
Post subject:  Re: Ebb and Flow cycle times and the effects on plant growth

Whats the fitting on the bell siphon made from. The air line bit.

Author:  trippytoads [ Mar 20th, '09, 00:24 ]
Post subject:  Re: Ebb and Flow cycle times and the effects on plant growth

Dufflight wrote:
Whats the fitting on the bell siphon made from. The air line bit.


The elbow is a brass fitting. The bell siphon is ABS 2" and the snorkel hose is some tubing that I had left over from some previous hydroponic system.

With regards to the flow I started to mess with it last night. It looks like if I put a small 'S' trap on the drain I can decrease the flow quite a bit. The only issue with that is that I have to be careful not to overflow the bed. The pressure it takes to move the air trapped in the drain causes the grow bed fill height to be higher than it would if the drain was at normal atmosphere.
I'm thinking that I might keep the 'S' curve or air trap and exaggerate it but I'll have to change the bell and the stand off so that the grow bed doesn't over flow.

My opinion on the cycle time being too fast is that I can't imagine it being a problem. It seems that if you could run a hydroponic float bed where the plant roots are submerged in water all the time but the water is oxygenated to the point of saturation then this system should be fine (for some plants). The current system does cycle. It does expose the roots to air and water. So if I can't get it to slow the cycle time down by much then I might just roll with this bed's behavior and then try and make the other beds work at a slower speed. This would at least give me something to compare to.

Author:  thorn [ Mar 20th, '09, 04:30 ]
Post subject:  Re: Ebb and Flow cycle times and the effects on plant growth

If your growbed stands are raw wood, I suggest to paint/coat them so they don't rot out if that is going to be a permanent structure.

Author:  trippytoads [ Mar 25th, '09, 01:01 ]
Post subject:  Re: Ebb and Flow cycle times and the effects on plant growth

thorn wrote:
If your growbed stands are raw wood, I suggest to paint/coat them so they don't rot out if that is going to be a permanent structure.


I'm a renter so this all has to go with me in about a year. I would love to have something permanent but it's not an option for now. I expect the whole wood structure to last only a few years at best.

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