Backyard Aquaponics
A place to discuss aquaponics

Hello all,

This is my first post here, hopefully many more to come. I first found out about aquaponics when I saw Joel's setup on Gardening Australia, I was blown away. Thought about it for a couple of weeks and then the Girlfriend and I decided to go for it and ordered the book.

Now, we am planning a system made out of 2 1000L drums (aka shuttle drums here, although I have seen them reffered to as bulk bins on the forums). One will be the tank and the other will be cut in half and used as the grow beds. The only issue I can see is I will have less growbed volume than tank volume, I may need to add some more beds.

How well would a flood and drain system work with one pump always on (from the fish tank), auto syphons on the growbeds and then a sump tank pumping back into the fish tank? The only thing I couldn't find in "the book" was flow rates, how often should the water in the tank be circulated through the beds? Once per hour, twice per hour (ie, for a 1000L tank, pump 1000L/hour or 2000L/hour)?

Any tips/hints/suggestions?

Cheers,
Nova

Nova - should work ok with one pump always feeding the beds and then a pump with float switch in the sump to return water to the tank when needed (ie when it dumps from the beds by auto siphon. Would need to make sure the sump pump could keep up with the water dump rate or have a big sump tank. Would also be wise to try and get the beds to run out of synch so that when one is dumping the other is filling. This will reduce the amount of water out of the fish tank at any one time. Water loss from fish tank in a flood and drain system is a major limiting factor IMHO unless the fish tank is really big (and grow beds not proportunate). Trying to run grow-bed cycles at different timing to each other looks to be one way to help this. Regarding turnover of water - I am not sure of the answer, but would think that more than once an hour would be desirable.

Thanks VB,

I was about to write that both the pumps are the same size, so the return should be able to keep up, but then I caught up with what you are saying. I wonder how much water would fit in a 400L growbed full of gravel? I was thinking of using 2/3 of a 44 galon drum as the sump, probably not big enough.

It would be hard to keep two beds out of sync, the water flow would need to be EXACTLY the same otherwise they would eventually fill and empty at the same time.

Some more thinking needed methinks.

Nova

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You are correct regarding water flow having to be exactly the same. This may be a challenge worth taking up though (by somebody) because I think a stepped flood and drain with auto syphons may be the way to go, but the more I think about it, possibly unachievable. Not only would inflow have to be the same, the syphon starting and stopping would have to be the same every time (which I imagine would be unlikely.

Just a quick one with regards to how much room gravel takes up, I think AA quoted 50% but I was going to check that when I put my gravel in, this is one of the reasons I have been measuring volumes and water flow rates.

Using one bed with no gravel represents two beds with gravel - tomorrow's task is getting gravel.

The other quick point on synching pumps out of phase (now there's a contradiction), this depends on the full flood and drain cycle, if the cycle is quick then synch is important.

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Do it - like 'Ell!

I would have thought the gravel would take up more than 50% of the volume. If it is 50% then surely all the flood and drain systems would pump the fish tanks dry to flood the growbeds?? I kinda assumed/guessed about 75% gravel and 25% water.

Nova

Here in lies the problem Nova. I think u will find that there is more than 25% water, though probably not quite as high as 50%.

Nova,
to expand on my "quick points" there is some figures here:
http://backyardaquaponics.com/forum/viewtopic.php?t=382

basically a 40mm drain pipe can dump at a rate of 5,000lph, with an eighty litre tank and pump rate of 2,500lph the cycle is 3 minutes (90sec flood, 90sec drain) synching would be CRITICAL.

Pump rate reduced to 400lph = 13:30 mins full cycle (drain 75sec), so there is now 12 minute window to play with.

just a few thoughts and yes I think it will be more than 50% also

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Do it - like 'Ell!

I may have missquoted AA,it may have been an approximation but I will find out by the weekend

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Do it - like 'Ell!

The media to water volume has been talkabout before. I think the conclusion was that it varied greatly frm media to media. Most simple way id for you to test it yourself. Get a 10Lt bucket and fill it with gravel. Then add water till it comes to the top. Then tip the water out into another 10L bucket. There you have it

Just be aware that a high percentage of expanded clay balls will float and throw this test off. I've found that after time about 80% will absorb enoguh water to sink.

Cheers

Steve

And welcome!

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Welcome nova.

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http://s670.photobucket.com/albums/vv70 ... ?start=all
http://forum.homeone.com.au/

Yes it was a 'roughly 50%' guess as it sped my cycle from 13 minutes to 8.

I think hydroton was 30% but do Steves test is easiest.

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Cool, thanks guys.

There is no doubt that the smaller the gravel, the less room for water there is. I will have to test it when I get hold of some.

Maybe with a large sump tank and a float switch, I can have more water available. Although I would then also need an override level switch in the fish tank so I don't over fill it from the bed return. Say 800L fish tank, 400L sump with 1200L of growbeds. That should allow 300 or so litres of water in the growbeds before the level of the fishtank drops.

Looks like I need to get another 1000L drum.

Nova

Nova, I am using a 600 ltr fish tank and a 600 ltr grow bed, and a 100 ltr sump in a flood and drain system.
The grow bed is filled with 10mm drainage gravel and it appears that there is around 150 to 200 ltrs of water needed to fill the grow bed right to the top.
It cycles in around 25 minutes.
Muzza

Thanks Muzza,

That gives me a starting point for working things out in my head. Seems I can start with a smaller sump tank (around 150L). Once I get some gravel I can see how it goes and then increase the size of the sump if I need more water.

Nova

_________________
My hovercraft is full of eels.