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flood and drain cycles
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Author:  johnb [ May 9th, '08, 16:21 ]
Post subject:  flood and drain cycles
I have read that the consensus for flood and drain cycles is roughly 15 min on 45 min off. That in itself makes sense but I am hoping for some more detail.

Does this mean that it takes 15 minute to fill the bed and 45 minutes to drain it again?
Is there any difference if the bed takes 15 minutes to fill, 15 minutes to drain and 30 minutes drying? or indeed 5 minutes to fill, 10 minutes to drain and 45 minutes drying?

I figure the once per hour cycle is fair enough but is there any difference in efficiency based on how long the bacteria are wet for? The extremes could mean the bacteria are getting a quick splash or a good soaking.

Cheers,
John
Author:  KudaPucat [ May 9th, '08, 16:26 ]
Post subject:  Re: flood and drain cycles
John, my system is continuous flow autosyphon creating the flood and drain.

So I have continuous inflow, and periodic drain.

My beds fill in 8 minutes and drain in 4,

so I have 8 on 4 off, then 8 on, with no 'drying time' this works a treat for me.

But there are many ways to skin a cat, so long as you start with a sharp knife.
Author:  steve [ May 9th, '08, 16:27 ]
Post subject:  Re: flood and drain cycles
john, there is NO real consensus at all!

F&F fills in 3 mins and drains in 1 hour.

has not shown to make much of a difference in any respect.

i'll qualify that with i even think that you'd be ok with the reverse, a 1 hr fill and a 3 minute "quick release"

what i WOULDN"T suggest is a dead period of neither filling nor draining. look at it this way, bacterial processing is going to happen only when the water is in contact (simply speaking) with the gravel. this happens while filling and while draining, but NOT when empty
Author:  johnb [ May 9th, '08, 16:54 ]
Post subject:  Re: flood and drain cycles
steve wrote:
what i WOULDN"T suggest is a dead period of neither filling nor draining. look at it this way, bacterial processing is going to happen only when the water is in contact (simply speaking) with the gravel. this happens while filling and while draining, but NOT when empty


This was what i was looking for. Now it all makes sense. :cheers: Thanks guys.
Author:  steve [ May 9th, '08, 17:32 ]
Post subject:  Re: flood and drain cycles
no worries, and only a 5 minute wait for the first reply! ;) better than macca's drive through :)
Author:  TXPower [ May 9th, '08, 22:06 ]
Post subject:  Re: flood and drain cycles
I was wondering the same thing, I timed my system (2 half blue barrel GB's and 2 blue barrel FT's balanced with a 4" PVC pipe and one pump filling both GB's) and the beds filled and drained 5 times in 1 hour. Most of that time is the flood part as the drain takes about 1 minute. I only have some mint, some onion and 2 tomato plants in just now and they seem to be doing ok. I could cut the pump output back a bit. What are ya'lls thoughts on the frequency of my F&D time?

Thanks,

TX
Author:  timmy [ May 9th, '08, 22:11 ]
Post subject:  Re: flood and drain cycles
my own preference is for quick flood and quick drain a couple of times per hour, purely because i think it oxygenates the water and the plant roots more.
as long as you are flooding atleast once an hour i don't think anyone has found negative effects on the plants or fish?
Author:  TCLynx [ May 9th, '08, 22:53 ]
Post subject:  Re: flood and drain cycles
Right, if the bed sits flooded too long and the water doesn't have much O2 in it, the plants will suffer. If the bed sits drained down too long and the media has a chance to dry out too much, the bacteria suffer and some plants might suffer for that too, especially if it is really hot.

Benefit of continuous run pump with auto siphons, some pumps are better off running all the time (as starting is usually the hardest part) while other are not. But continuous pumping means you can use a pump with a smaller capacity and you don't have to worry about a time failing or not being able to handle the current required by the pump for starting. (Big pump/cheap timer often spells burned out timer.) Drawback or continuous pumping, running the power all the time and you have to get siphons balanced with the inflow (which can slowly change over time as pipes get gunked up.) (I find the Flout gets round this rate issue quite well, just have to make sure the inflow isn't faster than the drain pipe can handle. But flouts take up a lot of space in a grow bed.)

Timers are easy and if you can still get enough flow with a small pump to use a timer for flood and drain, then you can save more electricity but when the flow is off, there is no aeration for the fish. If the timer malfunctions, be ready for HSM.

I suppose all that had nothing really do to with flood n drain times. My grow beds flood and drain when they do, I've not really timed them since each one is a little different because I've tested out different drain and siphon methods on different beds.
Author:  Tony From West Oz [ May 10th, '08, 00:00 ]
Post subject:  Re: flood and drain cycles
As I am on a RAPS system, to minimise loading on the system when the dun doesn't shine, I have reduced the night time flood rate to 15 minutes in 3 hours, for 9 hours of the night, then once either side that at 1.5 hours then all day at 1.0 hours between starting flood cycles.

My nutrient levels are all close to Zero with 100 or so 100 - 150mm Rainbow Trout in my 5KL tank with 1KL of GBs planted with a variety of veggies.

I do not see any need to change the night time flood frequency as everything is rolling along nicely.

Regards,
Tony
Author:  Outbackozzie [ May 10th, '08, 07:08 ]
Post subject:  Re: flood and drain cycles
I also have big gaps in my pumping cycles. I find the beds are fine even when left without water running for hours (obviously not during 45 deg days :D ).

If you are using timers, just start with a lot of cycles, then delete a few and watch for the water getting dirty / ammonia rising. You may be surprised how little pumping is required.

It is good insurance to run a seperate air source to the tank also.
Author:  steve [ May 10th, '08, 13:22 ]
Post subject:  Re: flood and drain cycles
OBO, yep, as always i try and tailor my responses to a newbie towards the fail safe..........

i actually agree that a empty dead time is fine, but not for a newbie who may well need as much of the struggling bio-filtration as they can get :)
Author:  himzol [ May 10th, '08, 13:56 ]
Post subject:  Re: flood and drain cycles
KudaPucat wrote:

But there are many ways to skin a cat, so long as you start with a sharp knife.


And a dead cat !! :) :)
Author:  KudaPucat [ May 10th, '08, 16:01 ]
Post subject:  Re: flood and drain cycles
himzol wrote:
KudaPucat wrote:

But there are many ways to skin a cat, so long as you start with a sharp knife.


And a dead cat !! :) :)


That can always be arranged :twisted:
Author:  gokul [ May 10th, '08, 16:16 ]
Post subject:  Re: flood and drain cycles
Outbackozzie wrote:
I also have big gaps in my pumping cycles. I find the beds are fine even when left without water running for hours (obviously not during 45 deg days :D ).
What's your growbed volume and tank volume ozzie?
Author:  Outbackozzie [ May 10th, '08, 19:16 ]
Post subject:  Re: flood and drain cycles
+1 for Steve :D

Gokul - Currently at 1000l FT to 400l of growbeds (4 x 100l blue tubs) with 12 trout and some goldfish in the sump (less and less every day, bloody cats).

also 4000l of FT's with 2400l of growbeds (umm... 24 x 100l blue tubs :D ) 250 ish of fish.

I agree with steve - pump as much as you can when starting out, until you figure out how much you need.

I also once a week or so, I run the pumps continuosly for 24 hours, gets the water crystal clear.
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