Backyard Aquaponics
A place to discuss aquaponics

Hi everyone,

I'm just setting up my first aquaponics system, reading as much as I can everywhere, as quickly as I can, but there's one Q I can't get my head around.

If I build a flood and drain system on a timer, so that it floods either every 15m, off 15, then on again, or 15 on 45m off.....that means that the grow bed which is essentially the biological filter, is only being used for 15 or 30 mins each hour!??? Is that enough to keep the nitrogen cycle active enough and taking out the nasties from the water?

I keep tropical fish tanks, and obviously keep the filter on 24/7, so it seems alien to me to only have the biological filter working for a small proportion of each hour on the aquaponics system. What's different here, does this work, or am I missing something?

Thanks for being kind to a newbie!

When using a timer,there will be a stand pipe that will dictate the flood level.At the bottom of the stand pipe there will be a hole that will allow the water to drain slowly (once the timer is off).So if you run the timer on for 15 mins on & 45 mins off,the water will fully drain within the 45 mins.But the water pump must be powerful enough to make the whole of the tank water pass through the grow bed within the 15 mins.That's where the bio filter is.
It's recommended to pass all of the fish tank water through the grow bed at least once every hour to sort out the Ammonia.

For timed flood and drain, what 7341 says.

With aquaponics aeration is critical. Draining the media allows all the gaps to be exposed to the air. This also helps turnover the water in the growbed and prevents "dead zones" where the water is stagnant. For timed flood and drain, the important points are that the drain is big enough that the bed drains completely in the allowed time, and that the pump will fill faster than the hole drains, so it will fill the bed completely within the allotted time.

Many people use flood and drain with bell siphons, or loop siphons with the pump running all the time so the grow beds flood and drain more quickly, and have water in them most of the time.

Others use a constant flood method where the growbeds are filled at all times. Some plants do not like this but usually it is due to lack of dissolved oxygen in the water because it is more stagnant. This can be overcome with air stones, which are a requirement for DWC where no media is used at all. Plants in DWC may barely grow without air stones. DWC requires additional biofiltration since it lacks the media growbeds.

Siphoned Flood & Drain is the way to go IMO.

As mentioned, in an ideal situation you should aim to turn your FT water volume over through the GB's every hour, to achieve an adequate amount of bio-filtration.

If you run timed F&D at the widely recommended 15 on/45 off cycle time, you only have 15 minutes every hour to get your entire FT water volume through your GB's, and as you've suggested, there may also be an extended period where the water is not in contact with the bio-filtration material (bacteria on the gravel), so not achieving optimum bio-filtration.

Whereas, with siphoned F&D the pump runs 24/7, so you can use a pump that is a 1/4 of the capacity of that required in Timed F&D, as you have the whole hour to get the FT water volume through the GB's, not just 15 minutes. It aslo eliminates a number of potential fail points, ie: (a). Timers (b). The continual stopping and starting of the pump, and (c). The small slow-drain holes near the base of the standpipe clogging, as these aren't required with siphoned F&D.

If you are reading up on bell siphons, especially if asking questions on forums and/or Facebook chat groups or similar, don't listen to people that tell you bell siphons are unreliable, there are a lot of uninformed or inexperienced people out there giving "advice" on aquaponics... A well designed, well built bell siphon is extremely reliable.

Excellent information and perspective!!

I have 9 bell siphons that have been very reliable. I also have three loop siphons that work very well.