# Dissolved oxygen meter



## Soilwork (9 Nov 2020)

Hi All,

Can anyone recommend a decent dissolved oxygen meter for less than £1000. Even cheaper would be better.

Cheers


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## dw1305 (9 Nov 2020)

Hi all, 


Soilwork said:


> Hi All,
> 
> Can anyone recommend a decent dissolved oxygen meter for less than £1000. Even cheaper would be better.
> 
> Cheers


The Thermo "Orion Star"ones are pretty reasonably priced. The <"A123"> is about £650.

cheers Darrel


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## Wookii (9 Nov 2020)

Though I can't personally recommend any myself, I did look into buying one myself a few months back, and Cole Palmer seem to have the best selection. They have a few meters within your budget, including their own branded NIST certified one:

https://www.coleparmer.co.uk/c/dissolved-oxygen-meters?N=32270412+2252466114&Ne=150797373&Ns=P_ListPrice_CPUK|0&format=json&rgn=P_ISUEU&rlg=en-US&uty=dflt

Hanna Instruments are a good brand too, and have a few in budget:

https://www.hannainstruments.co.uk/...ygen/portable-meters.html?dir=asc&order=price

Be careful looking at the prices though as some are for just the meter and the probe has to be bought separately, and the probes often cost more than the meter.


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## Soilwork (9 Nov 2020)

dw1305 said:


> Hi all,
> 
> The Thermo "Orion Star"ones are pretty reasonably priced. The <"A123"> is about £650.
> 
> cheers Darrel



Thanks Darrel. I’m guessing this needs a probe additionally?

cheers


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## Soilwork (9 Nov 2020)

Wookii said:


> Though I can't personally recommend any myself, I did look into buying one myself a few months back, and Cole Palmer seem to have the best selection. They have a few meters within your budget, including their own branded NIST certified one:
> 
> https://www.coleparmer.co.uk/c/dissolved-oxygen-meters?N=32270412+2252466114&Ne=150797373&Ns=P_ListPrice_CPUK|0&format=json&rgn=P_ISUEU&rlg=en-US&uty=dflt
> 
> ...



thanks for the heads up.  If I may ask, why did you decide not to buy one?


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## dw1305 (9 Nov 2020)

Hi all, 


Wookii said:


> I did look into buying one myself a few months back


If it wasn't for the cost they would be a recommendation for a meter that is pretty <"much "plug and play">. 


Soilwork said:


> I’m guessing this needs a probe additionally?


Yes it does, I've just looked and I had no idea they were that expensive for that model. We've had a meter/electrode to trial, and it has seemed pretty good. 

cheers Darrel


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## Wookii (9 Nov 2020)

Soilwork said:


> thanks for the heads up.  If I may ask, why did you decide not to buy one?



Ultimately I sometimes need to second guess myself when it comes to buying 'toys' like this, so I don't get carried away. Given the costs, I had to stand back and justify why I wanted one or needed one, and what benefit it would serve in terms of how it would change what I did with my aquaria.

I already try and maximise DO and I try to maximise surface movement for that reason despite the CO2 off-gassing the likely results. I also focus on obtaining good distribution for CO2 and ferts purposes, which would also therefore help distribute DO as well, so I likely wouldn't be able to increase DO any further by those methods.

I also plant heavily and aim to get my CO2 and ferts on point to maximise plant growth and therefore photosynthesis, which results in visible DO saturation (heavy pearling) quite early on in the photoperiod.

Finally I also use a Twinstar unit, which although a little controversial for its marketed purposes, I believe works beneficially for the purpose I use it, in adding additional DO to the system.

Long and short of it, on reflection I realised that buying a DO meter wouldn't actually change anything I do with my tanks, and likely be only a confirmation of what I suspect already - that my DO levels are already pretty good, and I'd likely not be able to get them much higher, short of maybe adding an airstone during the night (which I may consider at some point), or moving to a sump with a trickle filter.

All that left, once I'd distilled my decision process down, was the purely academic interest of finding out what my actual measured DO levels are in various parts of the tank at various times in the 24 hour cycle. That would be nice to do, if purely from a geeky point of view, but wasn't sufficient to justify the cost - not just the meter costs but also the regular membrane replacements at £40 each. Had the meters been less than a couple of hundred I may have stumped up for one, or indeed if I could hire one for a reasonable fee, I'd also consider that, but not at over £600 + consumables.


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## noodlesuk (9 Nov 2020)

I've used a few of the Thermo brand ones at work. These use optical fluorescence to detect oxygen, so the tips have to be replaced every few months, and they expire when not used. Bear that in mind, the cost of tips!


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## Nick potts (9 Nov 2020)

No useful input on meters. but curious what benefit these offers as they are rather expensive.

Could an ORP meter be used instead?? (sorry if that is a very silly suggestion  )


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## dw1305 (9 Nov 2020)

Hi all,


Wookii said:


> that my DO levels are already pretty good, and I'd likely not be able to get them much higher, short of maybe adding an airstone during the night (which I may consider at some point), or moving to a sump with a trickle filter


That was really where I ended up, and it was why I wrote <"Aeration and dissolved oxygen.......">, about <"~fifteen years ago">. It wasn't entirely <"well received initially">, but I think it has stood the test of time.


noodlesuk said:


> These use optical fluorescence to detect oxygen,


You can get galvanic probes, they sell one meter for aquaculture with them. Possibly a Hanna one? I'm busy for a bit now but I'll have a look later.
Edit: I've had a look, it was a Hanna one, <"HI -9147 - 04">.

You would need to run the meter as a data logger, or it wouldn't really help. Dissolved oxygen is different from everything else, even the shortest period of very low dissolved oxygen is going to kill your fish.


Nick potts said:


> Could an ORP meter be used instead??


You could, the data would <"need a bit of interpretation">.  There is <"also BOD">.

cheers Darrel


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## Soilwork (9 Nov 2020)

Wookii said:


> Ultimately I sometimes need to second guess myself when it comes to buying 'toys' like this, so I don't get carried away. Given the costs, I had to stand back and justify why I wanted one or needed one, and what benefit it would serve in terms of how it would change what I did with my aquaria.
> 
> I already try and maximise DO and I try to maximise surface movement for that reason despite the CO2 off-gassing the likely results. I also focus on obtaining good distribution for CO2 and ferts purposes, which would also therefore help distribute DO as well, so I likely wouldn't be able to increase DO any further by those methods.
> 
> ...



Thanks for the explanation.  I currently run an airstone and our methods are practically polar opposites.  I don’t use fertiliser or co2.   However, like you I want to keep the oxygen levels high but I want to do this with very little flow.  The airstone is great for this but they are noisy and encourage evaporation.  

I wanted to compare oxygen levels with an airstone with that of an overflow hang on back that drops water continuously from a small height. Like a small water fall. Since the water is pulled in then taken over some filter media and allowed to fall into the water breaking the surface tension.
If DO levels read similar or there’s not much in it I’d prefer to take this approach.  The splashing of water from above seems more natural to me and wouldn’t encourage as much evaporation. 

Darrel, would an orp meter be good enough to measure trends? For example to say, this method yields higher o2 that that method?

there is a video circulating youtube which shows that airstones are superior to the other methods in that video.  He does use an overflow filter but the output is level with the water line and spills across the surface creating very little disruption to the surface tension.


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## Wookii (9 Nov 2020)

dw1305 said:


> That was really ended up, and why I wrote <"Aeration and dissolved oxygen......."> about ~fifteen years ago. It wasn't very well received initially, but I think it has stood the test of time.



Great article Darrel - I can't imagine why it wouldn't have been well received?

A couple of quick questions:

With regards to the use of an airstone/diffuser as mentioned in your article, how small do the air bubbles produced have to be before their contribution to DO results more from direct diffusion into the water, that simply drawing low DO water from the bottom of the tank and displacing high DO water at the surface?

I know this is a 'how long is a piece of string question', but how much surface agitation is really required to fully saturate the water column? I would imagine the surface agitation we typically can achieve with a canister filter outlet is probably nowhere near enough, and significant surface breaking and turbulence might be required?


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## Wookii (9 Nov 2020)

Soilwork said:


> Thanks for the explanation.  I currently run an airstone and our methods are practically polar opposites.  I don’t use fertiliser or co2.   However, like you I want to keep the oxygen levels high but I want to do this with very little flow.  The airstone is great for this but they are noisy and encourage evaporation.
> 
> I wanted to compare oxygen levels with an airstone with that of an overflow hang on back that drops water continuously from a small height. Like a small water fall. Since the water is pulled in then taken over some filter media and allowed to fall into the water breaking the surface tension.
> If DO levels read similar or there’s not much in it I’d prefer to take this approach.  The splashing of water from above seems more natural to me and wouldn’t encourage as much evaporation.
> ...



A waterfall HOB filter should work well as you describe - the problem you have (if you run it on a low flow setting) is making sure that oxygen rich waster is distributed around the tank well enough.

Where the airstone wins out is it naturally lifts low DO water from the base of the tank displacing the oxygen rich water at the surface.

Heavily planting is still probably the best method of getting DO into the water column, even in a low tech. Even though I imagine you are unlikely to reach saturation, the plants contribution will be significant.

EDIT: I see you've discussed this already here: https://www.ukaps.org/forum/threads/oxygenation-via-plants.62296/#post-614476


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## Soilwork (9 Nov 2020)

Wookii said:


> A waterfall HOB filter should work well as you describe - the problem you have (if you run it on a low flow setting) is making sure that oxygen rich waster is distributed around the tank well enough.
> 
> Where the airstone wins out is it naturally lifts low DO water from the base of the tank displacing the oxygen rich water at the surface.
> 
> ...



As far as I can tell the water fall should work in a similar way if you can obtain the type of over flow filter that has a long intake pipe that sits in the lower portions of the tank. Water being drawn in then replenished with oxygenated water continuously should work across the full volume in a smaller tank.
Ive noticed both air stones and waterfall methods do brilliantly to break up surface film too and they don’t suffer from altering o2/co2 levels as the water line decreases/increases.  In other words, they keep things relatively stable. 
I can agree that plants would clearer be providing significant oxygen levels especially when pearling but in order for them to do so they need co2.  The airstone does provide a constant source of co2 but it is relatively low which means growth is slow plants as a main source of oxygen  suffer from diurnal patterns where o2 can become very low at night.

I don’t like canister filters because as you say they do little good for oxygen unless they are blasting at substantial flow rates but this is counterintuitive as the fish will require more o2 just to battle against these flow rates where there are no current breaks. But I guess it’s all relative as you could argue that oxygen levels are low at night because most livestock tend to be fairly stationary in the dark. The issue is that microbial actions do not stop.

Its and interesting subject nonetheless.


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## Wookii (9 Nov 2020)

Soilwork said:


> Its and interesting subject nonetheless.



It is very interesting I agree - a DO profile would be very useful to see, I would love to see the comparison. I guess it just comes down to whether the results would really change your plans, and whether you can stomach the cost for the meter?


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## dw1305 (9 Nov 2020)

Hi all,


Wookii said:


> Great article Darrel


Thank-you, I'm still proud of it.


Wookii said:


> I can't imagine why it wouldn't have been well received?


I've added a link in to the <"original post">.


Wookii said:


> I would imagine the surface agitation we typically can achieve with a canister filter outlet is probably nowhere near enough, and significant surface breaking and turbulence might be required?


Yes and no, laminar flow is really what you want in the tank, so that the water from the bottom of the tank is continually circulated to the gas exchange surface. If you are reliant on direct aeration, you need either a lot of very small bubbles with a long residence time, or significant surface turbulence.

It all comes down to the same thing in the end, the area of the gas exchange surface. This is also why wet and dry trickle filters are so good, they have a huge gas exchange surface area.


Wookii said:


> Heavily planting is still probably the best method of getting DO into the water column, even in a low tech. Even though I imagine you are unlikely to reach saturation, the plants contribution will be significant.
> 
> EDIT: I see you've discussed this already here: https://www.ukaps.org/forum/threads/oxygenation-via-plants.62296/#post-614476


That is it the real advantage is the 100% oxygen production from photosynthesis, air is only 21% oxygen, however much of it you inject.

cheers Darrel


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## Soilwork (10 Nov 2020)

dw1305 said:


> Hi all,
> 
> Thank-you, I'm still proud of it.
> 
> ...


Hi Darrel
Not the most accurate tests in the world but what do you think about this video?


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## dw1305 (10 Nov 2020)

Hi all,


Soilwork said:


> Not the most accurate tests in the world but what do you think about this video?


Yes, I think it is probably about right. There are a few minor caveats, was the temperature* the same? etc.

*edit: <"The meter"> has automatic temperature compensation

The thing we really don't know is:

We don't know the state of the inside of the canister filter. Because there is quite a large bioload, with messy "fish", and no plants my guess is that the <"water is becoming de-oxygenated"> within the canister media. I don't think you would have got such a rapid response from the DO meter otherwise. 



dw1305 said:


> ................Compared to using plants, attempting anaerobic denitrification in a canister filter is such a bad idea, I can't actually imagine why any-one would advocate it as a viable option............


If the filter is stuffed full of filter floss, and has a thick biofilm layer, it will definitely have quite a severe effect on dissolved oxygen levels, mainly because the filter won't be processing ammonia efficiently and that ammonia will be stripping oxygen from the water, because nitrification is an <"oxygen intensive process">.

Oxygen depletion is is very unlikely with a sponge filter, it isn't a sealed body (it has access to the tank water) and fresh air is continually being pumped through it.

cheers Darrel


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## Soilwork (10 Nov 2020)

dw1305 said:


> Hi all,
> 
> Yes, I think it is probably about right. There are a few minor caveats, was the temperature* the same? etc.
> 
> ...


I think thats the point really.  It doesn’t really matter about bioload and filter clogging etc.. because plants aside, this is probably of how 90 % of people run their tanks and its really easy to fall foul of the points you raised because people go quite long in between filter cleans.
With this being said my point is that it’s ridiculously easy to increase oxygen in the average tank just by adding an air stone.
I really wanted to test the airstone vs water fall and also an airstone vs a plant only system.

cheers


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## dw1305 (10 Nov 2020)

Hi all,


Soilwork said:


> .............It doesn’t really matter about bioload and filter clogging etc.. because plants aside, this is probably of how 90 % of people run their tanks and its really easy to fall foul of the points you raised because people go quite long in between filter cleans.


That is one of the reasons why I've pushed <"dissolved oxygen as being so important">. It was only when I started posting the cycling threads that I began to realise that there was a, <"pretty much total, disconnect"> between aquarists views <"on nitrification"> and waste water professionals, and that there was a <"lot of disinformation"> in the fish-keeping world.


Soilwork said:


> With this being said my point is that it’s ridiculously easy to increase oxygen in the average tank just by adding an air stone.


I think that is a very good point.

cheers Darrel


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## Wookii (10 Nov 2020)

How long do the increased DO levels, however they are generated, remain in the water column? With CO2 for example, even with fairly vigorous surface movement from a filter outlet, the levels don’t come down to atmospheric equilibrium even after 12 hours. Is DO similar?


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## dw1305 (10 Nov 2020)

Hi all,


Wookii said:


> the levels don’t come down to atmospheric equilibrium even after 12 hours. Is DO similar?


Diffusion of all <"dissolved gases is pretty slow">, which is why you need to maximise the gas exchange surface.  You can see that this is potentially a two-way street, leading to potential <"oxygen super-saturation in suitable conditions">.

You can process  wastes with really high BOD (or you can think of it as <"really large negative ORP values">) if  it you can get enough <"oxygen into them">. 

cheers Darrel


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## jaypeecee (11 Nov 2020)

Nick potts said:


> Could an ORP meter be used instead??


Hi @Nick potts

I use a combination of the JBL O2 test kit and an ORP meter. I find that the ORP meter gives a very useful indication of O2 level. As ORP is measuring oxidation-reduction potential, there is not one figure that I could give - all tanks will vary. But, I've done enough measurements now to know what to expect from my tanks. A typical figure would be around +200 mV and I consider +250 mV to be a good reading. I don't use ozone (O3) but measured doses of hydrogen peroxide (H2O2) will, as expected, increase the ORP figure. I still have more experimentation to do. My interest in ORP stems from trying to get a handle on dissolved organics (DOC/DOM).

JPC


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## Wookii (11 Nov 2020)

Soilwork said:


> Hi All,
> 
> Can anyone recommend a decent dissolved oxygen meter for less than £1000. Even cheaper would be better.
> 
> Cheers



Stumbled on this whilst looking for dissolved CO2 meters. No idea if it they're accurate enough for your purposes, but Extech models are a bit more budget friendly:

https://www.test-meter.co.uk/catalogsearch/result/?q=dissolved oxygen

Edit: membranes are also a lot cheaper at £25 for 10


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## dw1305 (11 Nov 2020)

Hi all, 


Wookii said:


> No idea if it they're accurate enough for your purposes,


My guess would be that they would do. 

cheers Darrel


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## jaypeecee (11 Nov 2020)

Wookii said:


> Stumbled on this whilst looking for dissolved CO2 meters. No idea if it they're accurate enough for your purposes, but Extech models are a bit more budget friendly:
> 
> https://www.test-meter.co.uk/catalogsearch/result/?q=dissolved oxygen
> 
> Edit: membranes are also a lot cheaper at £25 for 10


Hi @Wookii 

I have an Extech pH/ORP meter and it has served me very well for over five years. My understanding is that an ORP meter can be converted to a dissolved oxygen meter by use of a semi-permeable PTFE membrane and that's possibly what Extech are using. It's on my 'to do' list! I use the same principle when measuring dissolved CO2 except that I use the pH electrode in KH 4 solution and separated from the tank water by a very thin silicone membrane - it seems to work very well.

JPC


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## Soilwork (11 Nov 2020)

Wookii said:


> Stumbled on this whilst looking for dissolved CO2 meters. No idea if it they're accurate enough for your purposes, but Extech models are a bit more budget friendly:
> 
> https://www.test-meter.co.uk/catalogsearch/result/?q=dissolved oxygen
> 
> Edit: membranes are also a lot cheaper at £25 for 10



i think really I just need something that goes up when there is more dissolved oxygen available and down when there is less.  This looks like a good find.

thanks a lot.


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