Oxyge in water

[Jeff S]

I read all the time about the importance of maintaining adequate oxygen in the water. Is there a way to measure oxygen in the water?

[Leo White Bear]

There is a device called an oxygen meter, you can google it online but they are expensive and difficult to maintain.  Certian criteria must be followed to keep the bulb on the probe wet at all times and you must follow the directions to the letter.  I can't afford one of these units so I maintain the thought that incorporate as much atmospheric oxygen in the water and you are doing fine.  A good bubbler, which can be made for pennies and the drain water from your grow beds are all you need.  Check you fish for a while and if they are not gulping for air everything is good.  I have a bubbler which I made from an old plastic food canister with holes drilled in the cap and a hole for the air line drilled close to the bottom will suffice.  Insert the air tube in the bottom hole for about an inch and fill the canister with pH nutral stones to the top (I used aquarium stones) screw the top on and submerge this in your FT.  Attach the air hose to the compressor and plug it in.  You will see bubbles exiting the holes in the top and breaking the surface.  The actual surface breaking will allow oxygen to enter the water.

[TCLynx]

There are oxygen meters, they often cost between $300-$3000 and require their share of calibration and maintenance and well as understanding how to properly use them.

I think there are some Aquarium type oxygen meters that come with a whole control panel that test and monitor for other things as well and those whole systems probably run over $1000-$4000 but I don't know how accurate they are or how hard/easy to use.

There are also some dissolved oxygen test kits, most are not that easy to use (involve dangerous chemicals and acids) and some are not accurate.

If you are trying to run a commercial operation with large numbers of high value fish that need really high levels of dissolved oxygen (like a trout operation) then it is probably worth your investment in some higher level monitoring devices.

I think there are some aquaponics "engineers" out there working on some electronics for doing monitoring that might include some options of probes but I don't know about price, accuracy, nor even if any are in commercial production or even available as prototypes or for beta testing yet.

Most of us on a backyard or home hobby scale (who wouldn't go bankrupt and loose their job/business/home because of a fish kill) just rely on making sure there is some extra aeration for their fish tank and whatever else needs aeration.  There are rules of thumb about how much aeration to provide for a given volume of fish tank or square footage of raft bed and most bio-filters should indicate how much air needs to be supplied to function properly.  You can also observe your fish to see if there is need for more aeration.  One of the first signs that the dissolved oxygen level might be too low for them is that they won't eat as well.  Some types of fish will come up and gasp air at the surface if the situation is really dangerous.

Keep in mind that the warmer the water, the less dissolved oxygen it can hold while at the same time the demand of oxygen is increased by the elevated metabolism of everything living in the warmer water.

As long as the fish are not being tumbled about by the bubbles, it is actually difficult to have too much aeration for the fish.  That is different than super saturation of the water.  If you figure out some way to force more oxygen or other gasses into the water than it can normally hold at a temperature, it i super saturated and you do not actually want to expose your fish to super saturated water because it can cause bubbles to form in their blood stream kinda like a person getting the bendz from surfacing too fast from deep dives.  So the use of pure oxygen or special pumps that create micro bubbles under pressure to cause super saturation of the water is NOT to be done without learning and understanding the proper uses and how to do it safely for the fish.  If you are doing this sort of thing, then I'm sure an oxygen meter will be worth it to you since bottled oxygen or oxygen concentration equipment isn't cheap either and you would want to be using them as efficiently and safely as possible.

[Jim Fisk]

I have air stones from Walmart that are between 12 and 16" in each of 5 full size IBC fish tanks. (see my pics by clicking on my avatar) There are all sorts of quality air pumps for this purpose on Ebay but mine are out of surplus equipment from the dump and are industrial strength and very reliable. In a power outage I make sure I have the air pumps on a standby 12v/120v inverter and a truck battery for hours of life sustaining air. You can go many hours without pump circulation but air is vital. Normally I keep the water pump on the inverter as well but if it goes for hours (the power outage) I can double battery life by shutting down the water pump. Cheaper air pumps will go thru many diaphragms so I upgraded to free industrial pumps that go for years without a care. Not sure where to send you for such as my freebies go for about 250.00 used on Ebay. It pays to scrounge around the dump metal pile and junkyards if you know what you are looking at.

Here is a great price (49.00) for a 2 piston pump, that will give lots of air in deep tanks (most aquarium pumps will not) like my 330 gal IBCs, on Ebay

And here is the pic:Hope this helps

[Jeff S]

Is there any reason I wouldn't utilize my garage air compressor with a regulator for air in my tanks?

[Jim Fisk]

If it is an oil-less model you can but do you really want to hear that noisemaker going on all the time? Oil-less tend to be much louder than their oil lubed cousins but you cannot use an oil based compressor for breathing. And then there is the electric bill to consider. Also much harder to put that bugger on a bat BU system. That would take a rather large inverter. Just my thoughts.

[Jeff S]

Good points. The compressor is in my garage and would just have a hose running to the GH so noise shouldn't be a problem. As for cost it would only run when tank pressure is low so I'm not sure on the cost. The BU would present a problem. Not sure about the oil lubed issue. Maybe an oil separator would work. Just playing with ideas. Probably more trouble to seal the current air leaks in my compressor than it's worth.

[TCLynx]

Air compressors are designed to provide high pressure but generally minimal volume.

Blowers provide minimal pressure but high volume (as in they can run Lots of big air stones but only in really shallow water)

Air Pumps are in the middle being able to provide medium volumes at middling pressures.

Choose the appropriate tool for the job to get the best efficiency.  Look for depth or pressure vs volume charts to figure out which air pumps will provide the appropriate amount of air for your purpose at the best energy usage you can find.

In my systems, the shallow water (Raft beds) get their air from a blower and the deep tanks each have their own air pump.  When I can invest in getting the battery backups the fish tank air pumps will go on the backup but the air blower likely won't.  For now it's a manual switch over to generator to run what I feel needs to be run at the time.

[Jeff S]

What does the depth have to do with aeration? I've read that it's the bubbles breaking the surface that oxygenates the water. So confusing.

[Jim Fisk]

That has been in dispute for years. If that were true then why put air stones at the bottom at all? Why not just stir the surface? I'll go with "dwell time" meaning the longer the bubbles are in contact with the water (and the smaller the size bubbles) the more O2 is dissolved in said water.

Most aquarium air pumps are not designed for 4 ft. deep IBC FTs. The pump I showed above has no problem pushing the air to 4'. I have used both and I have a very nice large aquarium vibrator type pump sitting on the shelf because it could barely produce a bubble at 4' depth. It will work fine in a 12" raft bed however. For IBCs you need a motor driven oil-less pump. I raise Trout which need plenty of O2 and they are very happy. Blowers are expensive, noisy and very costly to run in my experience. Nothing pushes air like a simple motor driven piston when it comes to efficiency in a less than commercial system. There are the solenoid types you see everywhere on Ebay but they are reported to be deafening and not nearly as reliable as a commercial duty pump as seen above. We could debate this all day long but I have been aerating everything from fish ponds to sewerless recycling toilets for 30 years and more and this is what I use.

One other pump is the type used on vacuum cleaners and Jecuzzis. They are 1 - 3 stage ventury style pumps and are popular on Jecuzzi tubs for the air function and being a brush motor are variable speed with the use of a standard drill style speed control. They could well be of use and the brushes produce a small amount of ozone that can be very useful to an AP system as well. I have worked on them on many a Jecuzzi over the years. Easy to find in a dump, etc. for free. I will play with them when I have time. Less than 100% duty cycle could be their downfall. Someday

Jeff Sullivan said:

What does the depth have to do with aeration? I've read that it's the bubbles breaking the surface that oxygenates the water. So confusing.

[TCLynx]

Depth has to do with the amount of pressure it takes to push the air down below some depth of water.  So if you want your air stones to be on the bottom of your fish tank, you have to make sure your air pump can provide enough pressure to also get enough air down as deep as that.  For instance, if you are using a very small aquarium air pump, try putting the air stone down into much deeper water than the 10-12" deep aquarium you usually put it in.  What happens to the air flow?

Those little aquarium air pumps often can't supply any air once you hit 24" deep and having your air stones floating half way up the side of the fish tank is not necessarily an effective way to provide aeration.

28" of water depth requires 1 psi of pressure and most large medium pore air stones require the equivalent of 10" of water depth to push air through them.  So if you had a fish tank with about 46" of water depth you would need an air pump that could provide enough air for your amount of tank or fish at 2 psi (46" + 10" for the air stone =56" which needs 2 pounds per square inch.)

If you are only dealing with like 10" of water depth like in a little aquarium or a raft bed, you won't need much pressure to push the air down to the bottom of the water.

Hence why water depth actually has a big impact on aeration if you are planing to use air stones on the bottom of the tank to provide that aeration.  Also keep in mind that venturi type aeration methods will restrict the water flow and may still require an air pump if the venturi is placed deep enough that the natural suction can't pull the air down deep enough.

Surface area of the water is where much aeration happens but if something is on the surface of the water that blocks the surface to air interface (like rafts) you loose that aeration and have to provide it by other means.  And simply relying on a pump spray bar for aeration means that you need to keep that spray bar unclogged and if the pump dies or power goes out there isn't any backup.  Having a separate pump providing aeration is a means of redundancy and having that separate pump on some form of power backup is further "safety" or redundancy.  However, choosing and sizing the equipment appropriately is going to be very important for efficiency, especially if one wants to run it on an inverter and battery backup.

Having a large compressor motor kick on/off all the time is likely to be way too large a load for most reasonably priced inverters.

[TCLynx]

hay Jim, there are Diaphram air pumps that can handle pumping plenty of air into an IBC (The pumps I use on my 1000 gallon tanks are able to provide almost 2 cfm at 2 psi for only 50 watts of power use.  For a single IBC tank I would use the smaller 35 watt version of the same pump or I expect I could run 2-4 IBCs from a single one of the larger air pumps depending on the depth of water in the tanks.)  They have the drawback of needing their diaphrams replaced yearly but that isn't outrageous. 

I run simple 50 watt air pumps for each of my 1000 gallon fish tanks.  Perhaps if I were running trout I would want more aeration but trout are really not an option here anyway.  The size of these air pumps might be a touch small for my tanks (probably more appropriate for an 800 gallon tank at only 46" of water depth but that is only really of concern to me if the main pumps stop for an extended period of time during warm weather, at which point I would probably be plugging the water pumps into the generator for periods of time to circulate the water anyway.)

Now if you have a whole bank of IBC's being fed off a single air pump I could well see running a larger motor (read more electricity) to drive a piston pump but for people who don't know what they are looking at, NOT ALL PISTON AIR PUMPS are created equal.  And if you don't know where to get good working ones inexpensively or how to maintain them, it might be cheaper to buy a whole new diaphram air pump yearly.  Remember to calculate the ongoing electrical costs in addition to the pump cost and the regular maintenance costs.

I run a separate blower to provide large volume of air to my shallow (low pressure) raft beds.  That blower won't push any air out an air stone in a 46" deep tank and to get a blower that could provide enough air to the deep water at the same time as providing air to the shallow beds would cost me big time in ongoing electrical costs (would run well over a kilowatt all the time)  The smaller blower is well under 300 watts and each Large fish tank air pump is only another 50 watts so by using the most appropriate pump for the job I'm saving well over 500 watts all the time.  Also, I won't bother trying to run the blower if there is a power outtage since it would require too big an inverter to put on battery backup so I only need to worry about the fish tank air pumps.

[Leo White Bear]

I need to reply here pertaining to water oxygenation from air stones or bubblers.  A very small amount of oxygen DOES desolve into the water column from the bubbles but the majority of oxygenation occurs by the surface tension be broken. 

Example #1 Rain oxygenates the water just by breaking said tension.  Rain does not penatrate the surface of water to much depth, the surface is broken and thus the water is disturbed and oxygenation occurs.

Example #2 Waves actually do not penetrate the water column by much depth either (excluding storm action).  Common waves (less than 2' caps) break the surface and in turn add oxygen to the water area.