Backyard Aquaponics
A place to discuss aquaponics

the belief that growbeds with flow and drain not only provide air to the plant roots, but also also provide good aeration for the fish water, is generally accepted on this forum
I believe in it too
but there seem to be an uncertainty of the effect of filling/draining speeds on this
has anybody ideas on what would be best: fast filling/slow draining, equal filling and draining times, slow filling/fast draining or fast filling/fast draining with a pause between fillings/drainings (can be obtained by timing the pumps action)?

please argument as much as possible, not only with experience (extremely valuable), but also with why you think one system would be better than another for either plants or fish

frank

Currently favouring intermittent continuous flow.

Hahahaha ...

I think the fast drain (basically the splashing effect of the water leaving the grow bed and splashing into the sump or fish tank) probably gives the best aeration to the fish water while the simple flood and drain action at whatever speed takes care of the roots.

Perhaps it might be even better for the plants (at least some kinds of plants) to have a prolonged drained period especially if a more water holding media is used (sand, wood chips, coir, etc.) but I have not found such to be necessary at least in my systems. If the idle times are too prolonged, the filtration or aeration to the fish tank could suffer depending on the stocking density in the system.

A fast flood into a grow bed might provide some extra air but the splashing and perhaps spraying of water onto the surface of the media, plants and even out of the system would not be worth it IMO.

I like the slow fill and fast drain since it can accomplish the flood and drain effect using a continuous run pump without worrying about timers, float switches or other failure prone components. It can also utilize a smaller flow and hopefully less costly to run pump while still filtering the same amount of water per hour.

A fast fill slow drain set up is often what a system using a timer to accomplish the flood and drain must be since the drain must be enough slower than the pumps fill rate to allow the pump to flood the bed. In this set up, I would probably run supplemental air for the fish tank since the water returning to it might be a small trickle with little splash to it.

It is all a balancing act of finding what works for a particular situation/system and the skills/methods/priorities of the operators of that system.

Concise and clear.. as always TCL...

Yep the "drain" is primarily about oxygenation of the roots... not doubt there is "some" oxygenation of the water as it does so...

Primarily it's the return to sump/tank that provides the oxygenation to the water.

Flood, drain rates... as you say TCL... depends somewhat on the media.. and the design of the system...

I prefer slow flood, fast drain (by looped siphon)... as I pump continuously...

Slow flood/slow drain... can present problems with some media... i.e. vermiculite, coco coir IMO... as they just stay too wet...

Some plants may benefit from this... most don't... and some just hate being too wet ... too often... i.e strawberries...

If we think in terms of a "natural" environment... then plants benefit from regular consistent "flood" (rain)... followed by a period of "drain" (drying)....

Again primarily for reasons of oxygenation.... plants that have been flooded or submerged for extended periods... often look "wilted".... because the lateral oxygenating roots have been able to take in oxygen...

Paradoxically... watering after a long period of rain actually helps reoxygenate the roots... mainly, I think, by washing off soil and debris that has adhered through the extended flood...

I've been using coco coir and concur with Rupert, the stuff stays too wet. It's been on continuous flow, loop siphon but I have to change that (what's the easiest way to convert from continuous/loop siphon to timer?).

I'd like love to find a way to use coco with continuous flow, as there are many benefits with this medium. I can get half coconut shells for 50 cents a sack. I'm considering getting these and using much bigger pieces to allow for better aeration.

It's definitely a balancing act, like most things in AP.

You might be able to stick with it Plachon.... just put your pump on a timer and ajust the "on" cycles to your weather, and how wet the coir is....

Only way to use the stuff IMO... I have my strawberry towers based on coir... and a timer... with drip feeds...

I was thinking about that, but what if the power cuts out while the GBs are filling? They wouldn't be able to drain until the next session.

That's true.... but just as true, no matter what other way you do things...

And if you're powers out... I'd be concentrating on keeping the fish alive... not worry about the plants having wet feet for a while ...

I think I'll end up converted 2 containers to timer and 2 continous. I will try some of the really big coco pieces with plants that like water. Ultimately, I'll probably have grow beds with timers and some NFT to continuously flow and keep up the oxygen.

Hi Frank,

I favour slow filling and fast draining to draw through the oxygen. Without any experience yet it is merely my perceived preference. This I believe would give the plants time to absorb moisture and then a rapid exit would draw down oxygen. I suspect this is best for earthworms too. Slow drain might be too wet for them.

I want to use a media that has very convoluted edges..... so encaptured moisture levels will still be high after draining. Also good for earthworms I think. I am completely sold on earthworms now.

I would only like to achieve 1 cycle per hour. I have no idea yet how long my GB would take to fill, but plan to use enough SLOs out of the Fish Pond above to get this broadly to within this parameter. With rough grow media that holds droplets in its convolutions I don't think the flooding needs be too long....(I would be interested to know what most filling times are)..... weather will have to be taken into consideration I suppose..... time will tell ....

Just a thought for coco beds, don't know if it would work:

place a header tank between the tank and growbed with a small autosiphon in it.
use this to add water to the growbed in short bursts - this might allow you to run a slower fill rate (therefore less cycles/day) but still have enough inflow to the growbed to get the siphon to kick in properly. Should make the siphon break better as well.

Almost an intermittent continuous flow system Steem, I suspect Rupe thought it was just an oxymoron Was going to call it an intermittent pouring drip system, but that was just as bad.
Sorry for the hijack Frank (stick in a smiley with a contrite face)

by placing a tee in the pump outlet you can bypass the FT and return a portion of water back to the sump. regulating the amount of bypass water will change the flood interval. I shoot vor 45 min to 60 min. cycle. Additionally the bypass keeps some water in the sump to keep alive any fingerlings and reduce pump cavitation (running dry)