Backyard Aquaponics
A place to discuss aquaponics

Still tossing up whether to have a sump tank in my (as yet, virtual) system.
Basically I have the option to have the fish tanks below the grow beds and negate the need for a sump tank/pump/et al, but I'm wondering about a couple of things if I go that way.

a)What minimum gradient/slope should the drain from the grow beds be?

b)If there is no sump pump, is there a good fail safe way to make sure there's enough air dissolved in the water?

P.S. noise from water flow is not a problem - I'm in a semi-rural area.

Have seen a dam in bridgetown wa that runs a fountain, I have a fountain (much smallerin the middle of my smallish tank, but have just built it, but after a couple of days things look ok and plenty of aeration )

You can use a battery backup air pump and that will supply the fish with air.
Most systems I believe are level and water then changes through the system hourly or there abouts.

I have 3 half barrels as grow beds and 3 half barrels below for fish which are joined and overflow to the sump. I had an air pump to start with but the syphons from the grow beds to the tanks below force air in when the water breaks the surface. I've also got a T on my pump outlet that puts water back into the sump like a bleed valve (my pump is a lot bigger than I need so this is fully open) and that points downwards also forcing air into the water.

I haven't been running very long or with a lot of fish but they don't seem to be gasping for air like i've read they do when there's not enough DO. If you want a pic to help it make sense let me know. Basically if the flow of water breaks the surface of the fish tank, it should force air into the water.

jonezy,
I had vague thoughts of using excess flow from the pump to oxygenate - good to know someone has tried it already.
As for siphoning, does the drain pipe from the grow beds extend below the water level in the fish tank?

No I've got mine a few inches above the surface of the water. If the syphon pipe goes below the surface there won't be any air forced into the water.

je comprehend.

Uncle Yarra, have a quick look at my system http://www.backyardaquaponics.com/forum ... 7&start=75
I don't use a sump and the gradient for the return is minimal. It uses the height above the tank to assist the drainage. The tank is sunk 250mm into the ground and the beds sit at 600mm above ground level.

I use this method also. Both of my fish tanks have returns from the main pump which shoot water into the system. The siphon lines from my main two growbeds also sprays into the system, and one of my fishtanks has a three tier waterfall, which also gets the job done. I am hoping not to need an air pump on a normal basis, but just as emergency backup. I have 450gal fishtank, with about 30 mixed size bluegill and 45 small goldfish. Planning on another 50 bluegill of mixed size. Hope it keeps working.

I also have a way over sized pump for the system (got a free pool pump and sand filer) so I could probably have a water slide in addition to the water being pumped to the grow beds. Anyway, when the grow beds drain, that splashing helps with aeration and the flow through the sand filter is being returned to the tank in a steady gush..

I'm hoping that I only need air for the emergency battery back up. Which I better get soon as I just got fish!

An aquasonic airstone in each fishtank will help with aeration. These are about a foot long and give really good oxygenation with fine bubbles. This combined with the gravity return will give you plenty of air for the fish, assuming you are running comfy stocking levels. With your proposed 3000lt fishtanks you could easily grow out 150 silvers in each tank to 400 grams. That is only a stocking density of 20 kilos per 1000lts when they are at harvest size.
If you only drill one 6mm hole in your grow bed drain pipe, it will give an extended drain time; i.e. more oxygenation. The oxygenation occurs primarily as the water drains thru the grow media.
I wouldn't run an airpump as a matter of course, but by all means get a battery one as a backup in case of power failure.
Hope this helps.

TT,
So you reckon there'd be more air dissolved from a slow draining gb than one assisted by loop-siphoning?

(BTW, thanks others for comments/ideas)

test message only

Nope Uncle Yarra... I think TT is suggesting incorporating an airstone in ADDITION to aeration of the water return from your growbeds/siphons ... particularly as a backup (hooked to a battery maybe) in emergencies

Don't believe having an airstone running permanently would be "harmful" though and I'd be tempted to include one regardless... especially for those "hot" days.

Myself I believe a "quick" drain pulls the oxygen down through the growbeds better than a slow drain...... I feel it's better for the plants anyway....

As to whether a slow drain actually induces more oxygen into the return water.... not sure.....

But a faster drain more frequently... i.e greater water turnover/hour... would I believe

Uncle, I was more thinking that what oxygen was available, would be available over a longer period with a slower drain. As to whether it is a loop siphon or not, I would be inclined to run the standpipes, outer for protection of the inner for drainage. You won't get a biofilm buildup like you will with loop siphons, that will need clearing from time to time. (Bit of a pain in the butt.)
Standpipes are very easy to set up and it is a once only thing. Lotta photos on here to check them out.
I am inclined to agree with Rupe on the quick drain pulls down more oxygen for plants. I was more thinking about the extended splash in ur fishtank with the slower drain v the quicker drain. To answer this question definitively prolly needs some controlled experiments with proper DO meters etc.
BTW an airstone at low stocking densities is perhaps not completely necessary. For 30 bucks or so tho, they give piece of mind. (For instance DO drops during feeding. If ur airstone is running but ur pump is not, you know that things will still be fine til ur next pump cycle kicks in. They cost buggerall to run and just add some insurance.)