Backyard Aquaponics
A place to discuss aquaponics

I'm thinking of using O2 tanks for backup to FT, and am trying to figure out how to do it. Any help would be appreciated. Thanks!

What size O2 tank

Timmons Recirculating Aquaculture
Lekang Aquacultural Engineering

What size system and what densities are you running?

There is nothing wrong with using O2 for back up but for a backyard system it would be very expensive.

200 lb cylinder? What about O2 concentrators? Will they work. Only have the 1 -225 gallon fish tank currently, but plan on expending.

Expending lots o dollars on O2.

Seriously why do you want to use pure O2.

I initially thought it mat be an easier less expensive system to have in place for back-up. I know Ryan mentioned he used it during a prolonged power outage...something that is very possible here. I guess, just having a good generator and gas supply may be an easier options. I have access to tanks for welding, and thought if it wasn't too difficult, I could make a solenoid type actuator(12 volt) that would keep the fish happy when the grid went off for extended periods of time. We have lost power here for days at a time. Typically, during hurricanes(no solar) and getting gas during those times is impossible as well.

If you already have to have the tanks on hand then that makes more sense. If you already have to pay the leasing costs of the bottles the gas isn't so expensive especially if you don't actually use it.

I wouldn't use O2 without a dissolved O2 sensor and controller because how would you regulate the O2 delivery with any efficiency without such control? DO sesnors range from DIY kits at around $300 to $1000 plus controller, plus programming ($?) plus angle seat valve (~$100-300) better than solenoid).

A battery backup for long term outage could get really expensive but in combination with a generator not so much. Especially if you want power to your house post hurricane.

And you wouldnt have the fish densities to warrant it anyways.

I would like to push the densities up quite a bit.

O2 concentrators put out quite a bit of heat , the older the model the worse they are. Just a heads up. Also they dont put out 100% o2. At 2 liters it will be around 95% and at 5 , max on the standard models 90% is as good as you can expect. Again the older the model the worse this is. A standard e tank on 2 liters/ min will last less than 3 hours depending on temp. These are the 2 ft tall green ones you see on the back of wheelchairs in hospitals. I worked on them for five years at my previous job so if you snag one at a yard sale or "something". And have a question pm me and I'll help if needed.

A full 'E' size cylinder will last approx 5 hours at 1 litre per minute. There is also a cool formula to work out how much time you have left using the pressure reading in the cylinder. Each size cylinder has a different factor that you need to use and you could prob find that chart on the net. I do remember E size cylinders use a factor of 0.28 so the formula is PSI x Factor / Flow Rate = Minutes of oxygen left. The flow rate number you use is in increments of litres per minute.

Example would be, say your E size cylinder has 1600psi left and your flow rate is 4 litres per minute.

a. Multiply 1600 (your Psi) by 0.28 (x factor for E cylinder) and you get: 448
b. Divide 448 by your flow rate: 4, and you get: 112
c. You have 112 minutes of oxygen left

Its possible but so is using a forklift to drive coast to coast.

It takes serious amounts of energy to purify O2. RAS high density systems have to use pure O2 because that is one of the best ways of delivering enough O2 to the fish.

Systems that use air as their source of O2 can go as high as about <40kg/m3 for O2 sensitive fish and <70kg/m3 for fish like Tilapia but at those densities if anything goes wrong the fish will be dead very, very quickly.

Generally on this forum it is recommended that densities be kept at or below 25kg/m3. At these densities air is all you need and it is a cheaper form of O2 than bottled, concentrated or liquid. That doesn't mean you can not use those sources of O2 but I wouldn't recommend it.

Man seriously, it's got to be cheaper just setting up a small solar-battery setup with a few small airpumps eg:



For $300 materials here in oz you could build yourself a decent solar backup system. A 40 watt solar panel, 90 AH battery, a cheap 10A solar charge controller off ebay etc, which would power a couple of air pumps

I sware by the small 3 watt, 300 lph duel outlet air pumps you can get nowaday - 1 in a tank (eg IBC) puts out enough oxygen to sustain a tank full of fish for hours.. I don't know the precise ratios regarding o2 output etc, I just know this works as I run 3 IBC tanks like this

If you size it right you can just let it run 24/7 without needing relays etc. A permanent constantly running 'backup' air pump

at least that's my 2 cents, for what it's worth

Powerwise, running one 3 watt air pump continously you would have:

3 watt airpump + say 1 watt power loss through inverter (Doubt it would be this much, but erring on the side of caution)

4 watts x 24 hours = 96 watts

or 0.096 Kw drawn per day


Even the puniest little solar setup could handle that load. So just string a stack of them together to get the desired air output you need. I'm talking about the small aquarium airpumps most pet shops sell (some more efficient than others)

I'm convinced this is a more effecient and affordable approach than running one of those big chunkalunka monster airpumps, which make a heck of a racket and seem to lose a stack of effeciency through heat etc.. or co2 tanks and related gear