Backyard Aquaponics
A place to discuss aquaponics

I'm sure this has been asked before but I could not find anything on this subject. I am in the process of setting up a system but do not know what style of grow bed I should go for. I a tending to lead towards a flood and drain system but am also considering a constant flood system. What is the better of the two systems and what are the advantages and disadvantages of both systems.

constant flood is great.

F&D pros: if turning pump off can save some power.
cons: need huge sump, if using syphons they can stop working, during summer causes larger temp swings.

constant pros: normal/ no sump, works great.
cons: none basically.

Mega trial and thread

viewtopic.php?f=51&t=8621

I'm still a newbie but F&D ok if you have enough water for both the grow beds and the fish without running the tank dry.
Also good for completely emptying the water to allow more oxygen through the system.

Our system was expanded and converted to constant flood.....havenm't really had too many issues and I just pull out the stand pipe from the grow bed every now and then to completely dump all the water to try and avoid and dead zones/lack of oxygen.

Constant flood very easy to setup

only real con is that with a long-term constant flood preferential pathways can develop in the grow bed, and parts of the growbed can become isolated. In cases with top feed standpipes water flows mostly near the top of the media (so new water goes out too quickly). But this is easily resolved by simply [manually] draining the grow bed every now and again - even just once a week - helps to renew the water.

It is important with CF to make sure the water level is sufficiently below the top of media - else can affect plant growth and health. But works well (as per BYAP trails viewtopic.php?f=51&t=8621) provided these sorts of things are addressed.

A slightly more complex approach that works well is to use a Bell Siphon with a hole in it or no lid (so its no longer a siphon). An advantage with the design of the Bell Siphon is that it draws water up from the bottom of the GB.
So this concept can also help a CF system.


** A reasonable hybrid to address water volume issue is to use timer F&D (pump off for periods) but only part drain the bed. You can do this by having the hole partway up the standpipe so 25-50% or so of the water always stays in the grow bed. Provided you have a good distribution of feed water the new water will displace the older bottom water and push it towards the standpipe.

the issue of pathways comes up much less when annuals are being grown as everything gets disturbed at harvest time.

when a bed is planted with perennials for long enough, even a flood and drain can clog with roots so much that anaerobic areas can develop anyway. - much like the photo EB posted of that clogged bed.

anaerobic zones usually arent too much of a problem until disturbed, which can be remedied by taking the bed offline first.

all CF beds should draw water from the bottom no matter what, bell syphon installed or not, the media guard dictates where water is taken from.

Has anyone considered intentionally adding pathways to their grow bed? Set them up with a baffle system throughout?

Sounds like proper media guard installation will solve most water turnover concerns... where is intake usually handled... at the bottom of the media guard or a bit above floor level?

F&D aims to keep ~1" undisturbed for mineralization in the grow bed, should the media guard be designed with intakes at least an inch from the grow bed floor to promote the same thing in constant flood?

Nope F&D doesnt keep 1" for mineralisation, you simply cant suck every last bit out with a syphon.

the last bit of water left in the bed doesnt go anaerobic to mineralise in that manner, it is always being mixed, on both flood cycle and drain cycle.

Why choose now? If you make the sump large enough and install the plumbing in the right way you can switch back and forth. See if it matters for the plants - for some things it might and for others not . Most plants it doesn't matter.

I've always had slower growth on my constant flood (I'm actually replumbing it this weekend to make it F&D).


I've got them on the same flow, meter away from each other, but the F&D has 1.5x faster growth. Also, there are 5x more worms in the F&D bed.

But all systems work differently, and you can't assume what works for one will work the same for another, somebody could have it working the opposite for them.

But the biggest advantage to F&D is that the water gets to every piece of media, so your maximizing the filtration, nitrification area. In constant flood, the water will travel the route of least resistance which isn't using the media to it's max.

I'd advise to set it up for F&D, but you can just take the bell off if you want it constant flood

Really depends on the siphon design. Was looking at keeping the siphon outside the bed and using a 2" Uniseal though I suppose it might make more sense to just use the same size throughout for flexibility. Might find I want F&D in the summer to cool the water more and CF in the winter.

F&D will heat the water in the summer more.

How so?

more surface area exposed to hot air = more heat exchange....

Sounds good in theory... but over the years I have seen a lot of systems and I've found the worst for transferring heat to the water were constant flood systems running blue metal gravel... and the best at keeping the water cooler are flood & drain systems running expanded clay.