Backyard Aquaponics
A place to discuss aquaponics

The flood and drain I so often talk about, works by the use of level switches. There are no timers or valves, just two pumps that have automated low level cut out switches, this is where it gets a little difficult to explain..

The pump in the main tank has the floating cut out switch adjusted to exactly the right hight so that the when it pumps, it pumps enough water out of the main tank to just fill the grow beds with water. As the water level in the main tank has droped, the pump has then turned off due to the float switch dropping. So now the main tank level is down a little and the grow beds are full.

The grow beds slowly drain (over about an hour) into a drain tank that has the same pump with a float cut out. This drain tank slowly fills, then the pump turns on, pumping the water from the drain tank back to the main tank, till the drain tank is emptied and gets switched off automatically by the float switch.. This drain tank keeps switching on and off as it pumps water back to the fish tank bit by bit, slowly raising the level of the fish tank back up again as the water is returned. The water level keeps slowly rising in the fish tank untill it raises the float switch enough to turn the the pump back on again. The the cycle starts again, pumping water out of the fish tank into the grow beds.....



I know this may all seem confusing, bloody hard to explain too... Hopefully this pic may help a little, notice the float cut out switches above the pumps? The pump in the fish tank is actually sittin up on some bricks so that the cut off float is up higher than in this diagram...

Ahhh - float switches - now I get it - thanks Joel

I was looking at these things b4 thinking how useful they would be for something like this...




from here: http://cityirrigation.co.uk/acatalog/Pump_Control.html

Am sure there would be an Aussie equivalent somewhere...

More like something along the lines of this pump OzV. Pump and low level cut out switch built into one.

Joel,

Is it correct to assume that you use a drain tank in addition to your fish tank because the grow beds are not high enough to drain directly back in to the fish tank?

I planned to put my fish tanks into the ground at a depth sufficient to enable the grow beds to drain straight back into the fish tank. Do I need a separate drain tank and pump in this situation?

Thats right Gary, If you bury the fish tank there's no real need for a sump tank and return pump. Although you would definately be in need of an air pump if you have reasonably high stocking densities.

If you have your return lines just trickling back into the tank, they aren't adding a lot of oxygen, where as with a return pump, it's forcing the water back mixing lots of oxygen in as it's pumped into the fish tank...

Joel a few questions re the flood and drain system.

How fully do you floood the beds ?

I think I read some where you flood to about 20 to 30 mm below the surface to stop the algea growing on the exposed bed material.

If you are flooding the whole bed, is there any need try to distribute the water evenly across the bed ?

As apposed to just having the water enter the bed at one point

What time intervals are optimum for the "flood" & "drain" cycles

Should they be the same, or should the flooding be quick and the draining slow or vise versa ?

the reason I ask is that I'm tending toward the diagonally cut drums with a syphon tapped into the bottom most point of the drum, and the syhon loop external to allow for easy adjustment. In this configuration I see the advantages of the drums draining more completely, as well as the beds larger surface area.

I would think that the draining time would be a product of the diameter of the syphon tube - the diameter determining the flow rate.

I'm thinking of using 1/2 inch or 3/4 inch tubing and fittings for a lot of my pluming in the barrel type system as these sizes seem to be the standard for sprinkler sytems, and seem to offer the cheapest fittings & hose prices.

But if the "time to drain" is to long I may need to look at larger dia piping for the syphons.

Warren

Hmmm.... I was planning on a flood and drain system too, and no return pump because of the design... something like this?

Not planning on high stocking densities, plus plants in the pond, and now I think a bubbler as well..

That's it Stella, make gravity work for you, are the tanks square or round, if its round you could get more beds around the tank.

Also I would suggest a syphon loop at the drain point so the beds flood fully before they drain, with out it not all of the bed agregate will get wet.

for an explination of syphons see steves link

Auto Syhpon link here


Warren

Another point, so long as the beds are higher than the tank they can be located elsewhere, and guttering used to return the water to the tank, you could even fill the gutter with aggregate and plant into it as well

Warren

I've got a neat little spot to put the fish tank (round or square? not sure)and two grow beds as a small experimental system - however with the location there is the potential for up to three more same-size grow beds behind the first two, but if I do that I'll be wanting a bigger fish tank... That would require more return plumbing and a pump, I think!

The rest of the garden is staying as 'other veg' beds like potatoes etc - so locating the grow beds close to the fish tank will be required anyway.

I finished the book last night, now to plan, rethink, rethink, plan.... I was eyeing off a section of the other yard last night, wanting to take that over as well



I'll have to sit down and have a read of that syphon thing, I'm currently at work and not 100% clear about it

Hey, you've been doing a fair bit of work on your design Stella, Nice one.....

Warren, yes, flood to just under the gravel surface. It's a good idea to distribute the water at least a little bit over the gravel bed, otherwise any much pumping through with the water would end up in the one spot, better to spread it out..

So far as the flooding and draining, well, different people do it differently. Some flood suddenly and drain slowly others flood slowly and drain slowly. It's something that needs further investigation...

EB
How much water do your growbeds require to flood?..(how much does your water level drop?) With my mini system I found alot of water was required and only left 10cm (about 1/4) of water left into my tub... fixed the prob by connecting another tub 60L tub.....

When designing my new system, with lots of growbeds,using a 'flood and drain' it would require alot of water..Looking at the Speraneo's system they seen to use a continuous system?
LB

I'm starting to seriously consider continuous flow in favour of flood and drain, for a number of reasons. EB correct me if I am wrong - your continuous flow system still has only the 1 small bed? How big is that bed and how much water approx do you pump through it per hour? Do you use one of Ebara sump pumps for that system also? Have any of them burnt out yet by using them continuously?

I will have more beds, but am trying to work out the size pump needed for my continuous flow. Will probably have 4 of Murray's f'glass (500l) beds at the start and pump from a 3000-3500l tank. I will want to build in some room for growth, as I could theoretically have twice as many beds in the system. I am thinking that a big pond pump rather than sump pump might be the go. Something like this Web Page Name, but hopefully a smaller and bit cheaper model. These pumps are designed to run continuously and in situations where there are fish (no oil bath in pump).

It is 500watts (Steve how much would that cost to run per day). I assume that I would be able to cycle this type of pump through use of a timer if I chose to do that instead at some point (eg not running pump during some of the night to reduce temperature loss, or changing to a flood and drain).

To flood my 4 beds it takes about 1/3 of my fish tank, or maybe a little less. The Speraneos use flood and drain, my large system is based around the speraeos design with a few changes here and there, though the basic principles of how it floods and drains is fairly similar to what they use.

My little system on the back verandah used to have the same ebara pump, but I had to slow the flow down a fair bit with a valve as it pumped too much. Now I have swapped it over to a 60W pond pump so that I'm not chewing as much electricity. I blew the original ebara pump in this system after about 3 years, not too bad...

The ebara pumps are continuously rated, and this is an important thing to look for if you want to buy a pump. There is also a davey sump pump that I found at the local reticulation shop that is rated continuously, yet only 100W. One thing I like to keep an eye out for in a pump, is the size of the particles that it can pump. Many pond pumps clog their intakes rather easily, and your constantly having to clean their intakes. The 70W pump I've put in the new barrel system is like this, I've had to clean the leaves n much from it every 2-3 days so far.... Not very happy with this pump....

Oh the small bed is about 1.2m diameter, and the flow going through it at the moment, I'm afraid I don't know... The 60W pump I bought to replace the ebara didn't have much info that came with it, it was a cheapy without even a box.....