Basic Understanding of Dissolved Oxygen in Freshwater

[Bradders]

Hi All,

This is basic by some of the experts on UKAPS standards, but I did find it a compelling introduction to dissolved oxygen, which even I could understand! 😀

https://freshwater-aquaculture.extension.org/wp-content/uploads/2019/08/Dissolved_Oxygen_for_Fish_Production.pdf

It's not written for indoor aquariums, but I think this is a good general reading for Aquarists. There is an excellent section on predicting oxygen levels overnight while you sleep.

I have access to a dissolved oxygen meter now and am looking to do some experiments. Why? Because I love technology and experiments! 😱

Regards,
Brad

 

[dw1305]

Hi all,

..... but I think this is a good general reading for Aquarists.

I think so, too.

I have access to a dissolved oxygen meter now

<"What type?"> The only reason I don't recommend dissolved oxygen meters is <"just the cost">. Not everyone is a fan however and I've never done any real experimentation with them. I used to have <"incredibly polluted water"> to work with, and now I mainly <"work with pretty clean water">.

..... Just recently we tested a myriad of DO meters in the lab and the results were: they suck.

All kidding aside, the only reliable meter we have found and continue to use is a Hach meter, but these are > $2,000 USD. When I say reliable, I don't necessarily mean only accurate, but also precise. We've found that the meters require constant recalibration, and even with constant recalibration, their readings never seem stable or replicable ........

and am looking to do some experiments

This should give you some <"ball park figures"> and the quick and dirty temperature - %saturation - mg/L conversion chart.

cheers Darrel

 

[Bradders]

<"What type?"> The only reason I don't recommend dissolved oxygen meters is <"just the cost">. Not everyone is a fan however and I've never done any real experimentation with them. I used to have <"incredibly polluted water"> to work with, and now I mainly <"work with pretty clean water">.

Yes, well $2,000 is well out of my price range! (However, if I had that money you can bet I would buy one!!). The one I got was cheap (below) and I think at best it can be use as an "approximate" and "relative" testing tool. But I bet that the accuracy of these things for < £200 is no where near lab grade.

https://www.amazon.co.uk/dp/B0CC5HDW2J

 

[Bradders]

In terms of 'type' it the one that has electrolyte solution and you have to wave around in the aquarium to get a reading.

 

[dw1305]

Hi all,

But I bet that the accuracy of these things for < £200 is no where near lab grade.

That honestly <"looks OK">.

and you have to wave around in the aquarium to get a reading.

Calibration is just in 100% moisture saturated air, so basically you take a sample of RO water, put it in a beaker (where the probe is a fit), give the water a good shake and then place the DO meter in the oxygen (and water vapour) saturated air above the water surface and calibrate to 100%.



Once you've calibrated the meter you dip it in the tank water, give it a swirl and the dissolved oxygen diffuses through the gas permeable membrane to the sensor and gives you a DO reading. It looks like it has Automatic Temperature Compensation (ATC), but you can always use the chart.

cheers Darrel

 

[Bradders]

Calibration is just in 100% moisture saturated air, so basically you take a sample of RO water, put it in a beaker (where the probe is a fit), give the water a good shake and then place the DO meter in the oxygen saturated air above the water surface and calibrate to 100%.

Thanks Darrel. In the manual, it says to calibrate by leaving in the air. Do you think that is wrong?

 

[dw1305]

Hi all,

In the manual, it says to calibrate by leaving in the air.

OK, I've never known a meter like that, but it might depend on the nature of the sensor.

Do you think that is wrong?

I wouldn't have thought so, but you can always check with some aerated RO water. The 100% saturation value should be

..... for an aquarium at ~27oC and a barometric pressure of ~1015mb, will have a dissolved oxygen of about 8 mg/l,

cheers Darrel