Dissolved Oxygen Testing

[DeadFish]

Hi all,

The problem with measuring dissolved gases is that all the kit is fairly expensive. That was why the drop checker and pH chart was developed to <"estimate CO2">.

In terms of dissolved oxygen meters, they are <"easy to calibrate and use">, the <"only problem is the cost">.

I'll add in @DeadFish as they are probably the best person to ask.


Eventually I purchased a meter that measured pH, conductivity and dissolved oxygen (<"Hanna portable multi-parameter meter">). It has been good and reliable, but I wouldn't invest that amount of money (~£1600) just to use in the aquarium.

cheers Darrel

Thanks @dw1305

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. We tested a few meters last week, albeit rather uncontrolled. We would test a system in the same location, only removing the probe or pen for a minute. Then we did the same but also recalibrated. It went back to the same location, same depth, etc. and each reading was different, but not within the deviation of the meter itself. IE, we would get 4.6 ppm and then 2.1 ppm. The gap in the precision decreased with price. ha. The Hach meter was dead on with each test, with exception to minor variances in the 0.0X realm which are likely real variances in [DO].

This begs the greater question: From a practical perspective, what does it really matter? We can only influence DO by the mechanical means we have at our disposal and more than that is likely an exercise in futility. Unless a system is incredibly anoxic, [DO] will vary and is relatively easily altered. Increase surface agitation, increase flow, eliminate dead spots, remove the lid, and or use one of those fancy algae inhibitors. I understand the contention that the algae inhibitors are at best making a tiny difference in algae proliferation, but I do notice an overall healthier tank (esp. at start up) when using one. Whether or not the affect on algae is pronounced, I would assume the affect on DO is. Most notably, my fish seem more active, especially late in the photoperiod when CO2 is at maximum concentration. Plants seem a bit happier as well.

 

[Bradders]

Thanks @dw1305

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. We tested a few meters last week, albeit rather uncontrolled. We would test a system in the same location, only removing the probe or pen for a minute. Then we did the same but also recalibrated. It went back to the same location, same depth, etc. and each reading was different, but not within the deviation of the meter itself. IE, we would get 4.6 ppm and then 2.1 ppm. The gap in the precision decreased with price. ha. The Hach meter was dead on with each test, with exception to minor variances in the 0.0X realm which are likely real variances in [DO].

This begs the greater question: From a practical perspective, what does it really matter? We can only influence DO by the mechanical means we have at our disposal and more than that is likely an exercise in futility. Unless a system is incredibly anoxic, [DO] will vary and is relatively easily altered. Increase surface agitation, increase flow, eliminate dead spots, remove the lid, and or use one of those fancy algae inhibitors. I understand the contention that the algae inhibitors are at best making a tiny difference in algae proliferation, but I do notice an overall healthier tank (esp. at start up) when using one. Whether or not the affect on algae is pronounced, I would assume the affect on DO is. Most notably, my fish seem more active, especially late in the photoperiod when CO2 is at maximum concentration. Plants seem a bit happier as well.

I think that some of this is “man’s” need to measure everything! Which I have some sympathy for as good data (should) mean an informed reaction to that data.

And I am that man. 😂

 

[dw1305]

Hi all,

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

We use DO meters a bit, but nearly always in situations where <"dissolved oxygen levels"> are at (or <"near saturation">).

Because it is normally in natural water courses we can use <"a biotic index"> and this gives an extremely good proxy of the range of oxygen levels since we last visited.

Some non-essential conjecture.
First the bit <"we know">, that the nature of that <"microbial assemblage"> is <"fine-tuned over time"> to reflect the levels of ammonia (NH3) and dissolved oxygen in the water.

This would be conjecture, but I visualise the microbial assemblage in a filter in the same way that I think about the <"benthic invertebrate assemblage in a stream">. In clean water (water with a lot of dissolved oxygen and a low Biochemical Oxygen Demand (BOD)) you have a diverse assemblage of invertebrates, including <"Mayflies (Ephemeroptera), Stoneflies (Plecoptera), Caseless Caddis (Trichoptera) etc."> with Tubificid worms (Naididae) and "Bloodworms" (Chronomidae) etc present, but as a minor component of the assemblage.

As pollution (BOD) increases dissolved oxygen levels fall and you lose the more sensitive species from the assemblage. At the same time the number of Blood worm and "Tubifex" increases. As pollution continues to increase eventually only the haemoglobin containing Blood worms and Tubifex are left, and these often <"build up to huge numbers">.

The "Tubifex and Blood-worm" scenario is the traditional view of "cycling", with Nitrobacter winogradskyi etc representing Tubifex etc. If you only ever look at sewage treatment works? You never find the Mayflies.

Thank you, this is interesting.

This begs the greater question: From a practical perspective, what does it really matter? We can only influence DO by the mechanical means we have at our disposal and more than that is likely an exercise in futility. Unless a system is incredibly anoxic, [DO] will vary and is relatively easily altered. Increase surface agitation, increase flow, eliminate dead spots, remove the lid........

I'll be honest, I don't really worry too much about measuring dissolved oxygen levels (<"even though I'm obsessed"> <"with dissolved oxygen">). I just have processes in place to keep <"dissolved oxygen levels high">, without any single sites of failure or positive feedback loops.

cheers Darrel