Backyard Aquaponics
A place to discuss aquaponics

Hi all,

Just wondering what size air pump I should add if any to my system. Currrently 700L fish tank with 20 silver perch.
1 Bath tub grow bed.
20 mins on 40 mins off pump cycle ( I think moves about 250L each pump cycle).
Pump cycle from sump to fish tank generates LOTS of bubbles for the few minutes it runs.

I currently have a small 3W air pump from an old aquarium in there.

Fish seem happy and healthy at the moment (system is 4 weeks old). Although they do play in the air curtain quite a bit.

Water temp approx 26-28CC at end of day. Tank is currently getting a bit of sun, but I plan to reduce that soon.

i think the more air in there the better, I suppose if we all had do meters we could see what our levels were, but I would assume pretty reasonable if not saturated. However, your temps are pretty high so your DO will fall as they get higher. Hope that rambling helps :0

Any ideas on ballpark, would you say 4L/min or do I need to be looking at something more like 15L/min? I just need some guidance to the general size.

PS Good to see your website up and running.

cheers

how big are your silvers?

just little on at the moment 30-60mm

to be honest, I reckon you would be okay without an air pump in there. Esp with that stocking density. Best best would be to have a backup air pump or 12 volt pump on a failover switch for power failures, otherwise stick with your small pump if it is breaking the surface IMHO it should be fine.

ok thanks. Definately need a battery backup of some sort.

they will be fine until next summer skygazer,as long as u run that little aquarium pump overnight. Silvers will handle DO down to 2-3 parts of whatever they measure O2 in. Rainbow trout need twice that. Silvers love swimming in the return water. They will let u know if they are struggling by gulping at the surface. Playing in the return stream is just that, fish play in highly oxygenated water. Wish I had ur water temps.

TT:
I currently run aquarium pump 24hrs and also run my pumping cycle 24 hrs at 20mins on 40 mins off.

ebay has 1800L/hr 20W pumps for under $50 delivered. Is that what I should get when the time comes? I am keen to keep the power usage down but 20W is not much.

If you have a T return to your tank before going to the growbeds, you could then do a venturi system and do an injection of the air from the pump into the water in the return pipe. Give the return pipe a bit of lenght after the venturi, it will be increase the contact time in between the air and the water.

It would grandly increase your dissolution of O2 in the tank water without consuming to much power.
Anyway a backup is necessary if you don't want to kill your fish straight away. Have a look at the southafrican system in the members system to convince you.

sky, I picked up a 1500lt per hour pump from B for $59, so yours sounds on the money.
If u use loop siphons, you can run these small pumps 24/7. They run on an oily rag. You just need ur drain rate to be faster than ur gb inflow rate. Pretty easy to do, just a bit of mucking around with ur ball valve tap at the gb. They won't handle much in the way of solids so I have cleaned the inlet on the one in GHF system once already, only takes a minute. It has a 2 year warranty so i will be interested to see how long it lasts. Tipping 731 days.
This will help aeration and adding a venturi as suggested by amacafish can only help more.

And if you are still not confident in the air and DO issue, plug the air pump to the venturi it will push even more air into it.
Other wise break the flow coming back to the tank in the finest flows possible by running the water on a grid at a foot af the surface of the water. The water will charge itself of O2 by contact with air. The finest the flows are the biggest contact surface you have between air and water.

Lucky it's a leap year TT, you might just be able to return it

The guy at the Aquatic Eco Systems place was helping me understand air pumps a while back. He gave me some rough rules of thumb though I don't know the conversions to metric right off the top of my head. He recomended 1 CFM (cubic foot per minute) for 400 gallons water.
Pushing air 28 inches below the water's surface requires 1 psi and most air stones require another 1 psi so most pump information gives the CMF at 2 psi. So, if I need to aerate my 600 gallons with an air pump, I need one that can deliver 1.5 CMF at a little over 2 psi (my tank will be more than 28 inches deep.) These numbers may be assuming there is minimal splashing comming from any other source of pumping.

As a backup the most important would be aerating the top layer of the tank, no point in aerating the hole of it, specially if you're on a battery. Fish gather to the surface when the DO is low, just oxygenate the first foot under the surface.
Othewise take a very small water pump (4W and 500L/h) and do a shower spray head over the tank. You could pump near the surface and let the water fall like rain, this would oxygenate a lot and consume a small amount of power from the battery, it would then last longer.

Otherwise for permanent use, you'll have to go on a bigger pump and bigger money. Or you find a way to inject air from a venturi with a small water pump. To oxygenate by injection is the best ratio of disolution you can find.

Hope this helps. If you need more on injection, tell me and I'll draw something and post it here.