I am using flood and drain with a media bed. Pump is on all the time and is works very well. my only problem has been with my design of the bell syphons. I have too many and will change that when I harvest my crop.
The rule of thumb for siphon systems is 15-20 minute cycles adjusted by flow into the GB. I have a 300 gallon FT and roughly a 100 gallon (total) GB with roughly 40 gallons of water capability in it. My system cycles every 7-8 minutes mainly because if I slow it down the siphon doesn't work. However, if my system cycles 40 gallons every 7-8 minutes that's 8-9 cycles per hour X 40 gallons which puts me at just over 300 gallons per hour, the perfect amount if you want to cycle your water once per hour. This occurred totally by accident but it works. This is with the pump constantly running.
No, Constant flood, as I understand it, is not a form of flood and drain. Constant flood means the bed is always flooded, such as running over the top of a standpipe - always flooded - no drain. This is different from a setup wherein the pump is always running with a siphon periodically draining.
I don't know that anyone has actually shown that 45 flood/15 drain works better than some other ratio, or that any one ratio works better than others, for that matter. My beds flood in about 10 minutes, then drain in about 20 and that occurs about once per 4 hours. This works with a timer and indexing valve, no siphon.
George is right. Constant flood is not a form of flood and drain. As the name implies, there's no draining.
So, there's flood and drain and constant flood/flow. With flood and drain systems, you can break them down into either timer based or systems that use a siphon. Pump runs 24/7 with a siphon. I really enjoy bell siphons, but I understand that some people have trouble with getting them to work. Apparently, I got lucky and have had zero trouble with them.
One downside to using an autosiphon I'm noticing is that if my water level gets too low, my pump can run dry and stop my system from circulating. Definitely wouldn't be an issue on a timer based system. The pump might still run dry if you aren't diligent with topping your water off, but the water will drain back anyway.
Thanks for the responses! Jeff, yours really cleared up some math for me. I will have to crunch some numbers so see where I am at. Everyone else cleared up my definitions and I liked Franks post because (and correct me if Im wrong) it echoed another sentiment Id heard on another forum; how are the plants? Are the fish healthy? If so...chill and be happy!
Also here are my system specs which I will follow up with a picture!
My grow bed area and volume are (gunna get down to the 16th!) listed below. The grow beds are a 55 gallon barrel cut in half hot dog style.
2 grow beds at 20.9375" x 36.375"= 761.602
761.602/144= 5.289 total sq ft
volume: 34.81 cubic ft (used one of googles wonderful calculators).
Piping from sump to fish tank is 3/4" with a rise of 3' 10.5" until it hits a 90 (still 3/4") and then another 90 within 5" to drop into the fish tank. Fish tank is an upright 55 gallon barrel with the top cut off and a 2" SLO that comes out the very tippy top.
This drops immediately into a 90 and also is converted back into a 3/4" pipe. This flow is restricted by ball valves, and the autosiphons consist of 1-1/2" bells with 3/4" stand pipes.
The pump I actually dont know how big it is. I came to work one day and found a (literally, a milk crate had been placed by my front door...) full of pumps (small ones) and aerators and air stones.
About 2 months later I found a power drill on the side of the road. It was a pretty solid time in my life.
Anyways, upon further investigation of the pump, its an SDH 230 from sunleaves.com. .3 amps, 20W, max head 6.5' at 396gph. I havent been able to find a pump flow chart for it on the net. Any thoughts???
Sounds like that pump will do the job for you based on your plumbing #s. I have a 396 pump with a little more rise in my plumbing and it does the job. There's not much extra but there's enough.
If I might add my opinion. I think you are making this too complicated. Since I stopped worrying about how fast I fill or drain and also worry less about my chemistry, My fish are thriving and my plants are awesome, that is a first for me.
I agree on the fish but my plants don't seem to do as well in AP as in the dirt. They grow fine but not as productive. Of course I don't add any nutrients.
Jeff my plants are growing great but as you say they are not as productive.
Thanks for the input! Here is a picture of the system just to get a bit more of an idea of what Im working with.