Backyard Aquaponics
A place to discuss aquaponics

Anyone care to submit what they think to be the minimum depth of GB media? I understand it to be about 300mm.

The 30cm that is often quoted is based on 2 reasons. 1. It provides sufficient depth to provide stability for your larger plants like tomatoes, eggplant, some of the larger winter veg, chillis, corn etc etc

2. Depth provides some protection for the bacteria against heat and dryness. You would not be suprised that the top of a gravel bed gets extremely hot in summer when the sun is shining on it. Hot enough to cook an egg - I shit you not.

What should be understood though, is that this depth is not set and others will work, provided proper consideration is given to the types of things discussed above. Often one will try and work to the depth of containers that are readily available to them. For instance I have a number of 180 litre (approx) round poly fingerling tanks which I intend to set up one day as beds for some big plant (toms, eggplants etc). The depth of these is way more than 30cm - probably closer to 60cm. While I will not get the surface area per colume of GB media that I would get with 30cm beds, I have them available so would be silly not to make use of them. They will also provide good stability if I want to (for instance) grow a paw paw tree again .

Bare minimum for a decent system is 200mm.

This IS the minimum. Less does not work. More is better up until 500mm or so. I am using IBC's (1000mm deep) as the next stage, but only because I want the filtration, not nitrification.

I have set up some really tiny beds before on the little aquarium. It can be done but there are so many challenges that I don't recommend it.

Most of my beds are about 30 cm or one foot deep. This seems to be a very good depth to work with as you only need as much gravel as it takes to fill that volume. In some situations, deeper might be better (large perennials, trees) but for most annual veggies 300 mm seems a good standard. Some small, fast plants (lettuce perhaps) might be fine in shallower beds but managing flood and drain in say a 15 cm bed can be really challenging.

I do have a 6 1/2 inch deep bed. I don't use this bed the same way as the other beds though. This is my nursery bed. I use it for starting seeds, and rooting cuttings. It is only half filled with gravel to allow me to set flats and nursery pots into a zone where the bottoms will get wet when the bed floods. I find this bed does have some trouble with it's auto siphon since I haven't left much room for error or variation here. This bed probably only contributes a little bit to my bio filter since the gravel gets disturbed often and of the gravel that is not always under water (in the bottom never drained inch of most any siphon operated bed) much of it gets exposed to light.

Some people have used feed troughs for their grow beds. Most of these are not as deep as might be optimum. If you happen to have freely to hand, containers that are say 20 cm or more deep then it might be worth using them anyway as you already have them. I would not build or buy any containers less than 30 cm deep for the purpose of grow beds though.

Fish tank & sump size may also play a part in choosing GB's. If you don't have enough water to fill all the GB's and can't stager them then you are more likely to stay closer to the minimum depth. If you have too much water then going for deeper GB's is a better option.

I know we have had this disscussion before but why the 50mm limit. If the bed is getting aerated would it matter?

500mm - more is just not needed, however I am using IBC's for growbeds, but I dont know how good they are yet, so.....I'll reserve judgement for a couple of months

More wont cause any harm though.

Looks like that 100mm bed with the bottom 20mm constantley flooded that i successfully grew onions this year and a tomato bush last year is doomed to fail [somebody forgot to tell the plants] seriousley in ap there is no hard and fast rule for newbees 200 to 300 mm is safe in that everything works
Its a bit like 2 years ago when we all first started all the things you couldent do so far 80% have been proven wrong

To be fair F&F, that 'growbed' of yours is mixed in with a whole heap of other deeper growbeds. An entire system made out of 100mm deep beds will not work for years, full stop. It does not have enough bacteria stability, or solids handling capability.

Been there, done that.

I could add a 100mm growbed to my system now, and it will work fine. However remove all my barrels, and make everything 100mm growbeds, and all hell would break loose.

You are right there but all the other things [like the things that we were told we couldent do have been provern wrong] i still stand by , anyhow franks been a bit quite lately

Who's Frank?

And what sort of things weren't we suppose to be able to do?

Start talking airlift pumps and you will find out.

frank only meddles with subjects
he thinks he can make a contribution to for the benefit of all

on all other threads
he quietly sits back and reads and learns,

rapped in total awe of your infinite wisdom


glad to find out that you miss me

frank

lol

Good to see your still kicking. Like the 3rd person.
Duff sticks his nose into everything.