Grow bed depth

[TheNative]

I have read that 300mm is the minimum depth for a grow bed. What is the maximum? I am thinking of cutting an IBC in half and using both halves as grow beds. That would make the grow bed 480mm depth. Of course I don't have to use all the space, but what if I did? Would there be any repercussions?

Also, sorta off topic, if I had a grow bed to tank ratio of 1:1 then wouldn't that empty out the tank? I supposed it would be offset by the grow media. So how much drop would I see? If I was doing a 2:1 or 3:1 GB:FT ratio then how much drop would I see in the tank? Would I need to cycle the 3 GBs on a timer?

Finally, would there be any draw backs to using an outdoor pond if it was designed so that a lid could be put over it? I am thinking of using one as my FT as pond liners are cheap and perhaps being in the ground would help stabilize temperature.

[Murray]

Hi The Native,
Almost any depth of grow bed will work, but over time 300mm has been shown to work very well. It is pretty much the optimum depth to have.
One or two of the members here run beds that are 400mm plus deep...no problem.
Depending on the media used, water will take about 1/3 of the volume of the grow bed.
Ponds are ok, but in the long run tanks are a bit easier to manage.

[dufflight]

OBO uses whole IBC's as grow beds and they run fine. Going under 300mm has too many problems and no real advantages. I like the 300 to 600 gb's.

[TheNative]

Thanks for the info. This stuff is starting to sink in.

Another quick question about sumps. how does their volume factor into the GB:FT ratio? if you had 1000L of FT, 1000L GB, and 1000L Sump what would be the ratio? 1:2? or still 1:1? Do you not even include the sump into the ratio?

Really looking forward to the new Aquaponics Secrets DVD you have coming out Murray. I really liked the previous Aquaponics Made Easy DVD.

[RupertofOZ]

Generally... we don't factor the sump into ratio calculations...

[nick]

i found that it takes about 125litres to fill a 585Litre bed using 10 or 20mm gravel.

[Murray]

The 1:1 ratio is only a guide to get started with. It is not a fixed rule or anything like that.

[RupertofOZ]

The 1:1 ratio is only a guide to get started with. It is not a fixed rule or anything like that.

With the emphasis on.... "to get started with"....

IMO... the old suggestion of designing a system with a 2:1 ratio, from the start... is a much better approach...

If it can't be done from the start... stock lightly... or get toward that figure before the fish grow...

Having seen how the 2:1 ratio got abused, with little understanding of why it was suggested in the first place... any the continual decline toward a 1:1 ratio.... usually with twice as many fish...

I'm hestitant to endorse a 1:1 ratio as a starting point...

[Murray]

Sometimes we worry about misinformation or outdated info, but I can tell you we are in good shape here. (not to say we don't have anything to learn?)

Today I listened to a speaker from the US and the information being handed out was a long way off. Pretty poor really.

[TheNative]

Yeah you guys in the outback are ahead of us on this one. Not a whole lot going on here in the states with aquaponics. Most of the systems are indoor aquarium fish tanks growing lettuce.

I think there is still a long way to go with aquaponics. Still in it's infancy really. Have you seen the drawings from NASA of using hydroponics on the moon and mars? I'm sure it won't be long until they have to change those drawings to an aquaponics setup.