Questions about airstone's placement on dissolved oxygen

[Daniel]

On 12/1/2020 at 10:45 PM, Ken Burke said:

While not not the proper data, and insufficient to draw any conclusions, the early data is relevant as long as the temperature remained consistent.

The reason the data is not quite proper is that I just plopped all the sensors in the aquariums as soon as they had water in them. The data could be fine for all I know. But I will feel better when all the probes and sensors are all calibrated at the same time and give the same readings if I put them all in the same beaker. The data could still be crap, but it will be very uniform crap.

On 12/1/2020 at 10:45 PM, Ken Burke said:

when you are taking your measurements, how do you control for stratification in the tank.  In case I’m saying it wrong - are you measuring in a “hot spot” where the dissolved O2 is higher?  (I’m guessing you have already accounted for this, but worth asking)

As for the stratification question my thinking was to put the airstone in the far back corner near the probes and put the dissolved oxygen sensor in the front corner diagonally across from the airstone. That way the airstone and the DO sensor are are far apart as you can get in a 10 gallon aquarium. Not sure if that is the right way to do it, it was just the first thing that came to mind.

Amazon is now saying all the probe calibration solutions will be here tomorrow and despite previous experience I do believe the package will arrive tomorrow, the tracking just look right this time.

[Daniel]

And then there are the unknown unknowns when it comes to variables. 🙂

[Daniel]

Step 1, Thermometers calibrated.

Calibrated to a NIST traceable thermometer accurate to 0.1°F

[Daniel]

pH probes calibrated.

This reading is pretty good. They are all in the same aquarium.

[Daniel]

Finally, replacing the membrane and cleaning the dissolved oxygen sensor.

[Daniel]

And after some further settling in on the probes, I'm happy.

[Streetwise]

Looks good! Did you enable the Temperature compensation setting for the pH probes?

[Daniel]

45 minutes ago, Streetwise said:

Looks good! Did you enable the Temperature compensation setting for the pH probes?

I did! Thank you for the heads up.

[Daniel]

Everything is now calibrated included the dissolved oxygen sensor.

The aquarium on the left has an airstone near the bottom. The aquarium in the middle has no airstone. The aquarium on the right has an airstone near the top.

Both airstones are powered by new USB Nano pumps with new Ziss airstones torqued to the same tightness. Both airstones are have the same length of tubing between the USB Nano pump and the airstone. Both USB Nano pumps are on the same power source.

That's all for tonight. I will start again tomorrow to collect proper data.

 

[Daniel]

Just thought readers of this thread would find these 2 tables interesting.

and from the Office of Space Science a the University of Wisconsin this handy chart.

There is a lot of research on the needs of game fish and commercial food fishes, somewhat less research ornamental fish like we keep.

 

[Daniel]

Just as @James Croney suspected a deeper airstone allows for greater dissolved oxygen.

Back in the 1970s I was taught that what an airstone did was agitate the surface of the water thereby allowing the carbon dioxide to escape, meaning that an airstone didn't actually add much oxygen to the aquarium, it just reduced the amount of carbon dioxide. This appears to be contradicted by these data.

But the difference between a shallow airstone (2 inches deep) and a deep airstone (10 inches deep) doesn't seem to be significant. In fact the aquarium with no airstone would appear to have more than enough dissolved oxygen for our fishes requirements.

But the airstones definitely create a flow of water that doesn't exist in the aquarium with no airstone. And all 3 aquarium have nothing in floating at the surface. I think today I might add a duckweed cover to each aquarium and see what that does to the numbers.

So James, put your airstone where you find it most aesthetically pleasing.

[Coronal Mass Ejection Carl]

Isn't 13.2 mg/L over 100% saturation?

I can't get anywhere near that.

My main tank was dipping below 4 mg/L during some parts of the day and struggling to get over 5 mg/L despite a wet/dry filter that should be one of the best types of filters in terms of oxygenation.

Dissolved oxygen was between 6 and 6.3 mg/L after adding the air stone,

Temperature ~77.5 F.

[James Croney]

@DanielAmazing!

First, thank you for the time, equipment, and dedication to this experiment. Together, we are stronger.

It does indeed look that the depth only accounts for 1.2ppm of DO in this setup. That's great news for me. I believe I can safely have a 'high stoned' tank and not risk my fish suffocating.  This enables me to use an airstone in a way that does not create a lot of turbulence in the water, and so is great for imitating a puddle or pond.

My duckweed should be happy, as well as the guppies I have in the tank. My feeling is that guppies in general would like a lower flow, but that is probably more based on what I think running in a dress would feel like, what with the big fanny fins and all.

As far as my non-scientific experiments go, they seem to agree with your data. My 'high stoned' tank is having none of the oxygen problems that happened before, without the airstone.

Would you be able to recommend any donation links I can throw some coffee cash at? Just to keep the wheel spinning.

-- in the future, I need to go to home depot and work out some riggings to test airlift pumps. My aquaponics stuff currently is "air lift assisted" with a pond pump, and it really kicks up the head height for me (above 6 feet). I'm not sure how one would actually use an airlift pump in an aquarium, other than maybe extending a sponge filter to the 'near top' of the water surface. I would guess that move water moves into and out-of the sponge when the top tube is closer to the waters surface. Having is lower would cause ejected water to be sucked back in maybe.  Ill get something going here when I can get a weekend free from work.

[Daniel]

7 minutes ago, Coronal Mass Ejection Carl said:

Isn't 13.2 mg/L over 100% saturation?

I can't get anywhere near that.

My main tank was dipping below 4 mg/L during some parts of the day and struggling to get over 5 mg/L despite a wet/dry filter that should be one of the best types of filters in terms of oxygenation.

Dissolved oxygen was between 6 and 6.3 mg/L after adding the air stone,

Temperature ~77.5 F.

I was really surprised at those numbers too! I know it possible to have over 100% saturation as I see references to it in the literature, but I was still surprised the see it in my results. But, in an aquarium with no airstone the DO sensor gives textbook numbers of 9.0 mg/L at ~69°F.

The water itself is brand new RODI water with a little bit of Kent R/O Right to give some minerals back. This shouldn't make a difference, but I thought I would throw this out there. Barometric pressure is currently 30.01 in and the aquariums are at 420 ft above sea level.

Can't rule out sensor calibrations issues though so I will recalibrate again in a few days and see what the numbers look like

[James Croney]

37 minutes ago, Daniel said:

Back in the 1970s I was taught that what an airstone did was agitate the surface of the water thereby allowing the carbon dioxide to escape, meaning that an airstone didn't actually add much oxygen to the aquarium, it just reduced the amount of carbon dioxide. This appears to be contradicted by these data.

Well, I would say half contradicted maybe. It does seem to be the case that the depth does not matter "that much" (1ppm@10inches) so I would think that the remaining 3-to-4ppm of DO boost was achieved by surface agitation of some sort.

I can also form the thought from the data that airstones may only 'need' to be run at night in a planted or otherwise highly bio-active tank. I wonder what the ill effects of over-oxygenation are... (not that we need to test this too, just thinking)

As with most answers, I end up wondering more things. ;-D

Again, thanks or the effort.

[Daniel]

4 minutes ago, James Croney said:

I wonder what the ill effects of over-oxygenation are... (not that we need to test this too, just thinking)

Over oxygenation (DO above 110%) is not good for some fish. I have read that it may cause 'gas bubble disease' which apparently is like the 'bends' are for humans.

 

[Daniel]

47 minutes ago, Coronal Mass Ejection Carl said:

Isn't 13.2 mg/L over 100% saturation?

I can't get anywhere near that.

My main tank was dipping below 4 mg/L during some parts of the day and struggling to get over 5 mg/L despite a wet/dry filter that should be one of the best types of filters in terms of oxygenation.

Dissolved oxygen was between 6 and 6.3 mg/L after adding the air stone,

Temperature ~77.5 F.

@Coronal Mass Ejection Carl is an asset to this forum. He gave me heartburn at first like when I would make some pompous pronouncement and he would quietly poke holes in it with an incisive question. But someone has to be there to help separate the wheat from the chaff. Having quality feedback like that makes the forum a more valuable resource.

[Maggie]

This is fascinating though I don't understand it all! I wonder how much the difference is in a 24" deep tank? I felt mine could have a "dead spot" on one side (HOB on other side) due to the depth. I feel better having a sponge filter there now, especially for the bacteria.

[Coronal Mass Ejection Carl]

1 hour ago, Daniel said:

I was really surprised at those numbers too! I know it possible to have over 100% saturation as I see references to it in the literature, but I was still surprised the see it in my results. But, in an aquarium with no airstone the DO sensor gives textbook numbers of 9.0 mg/L at ~69°F.

The water itself is brand new RODI water with a little bit of Kent R/O Right to give some minerals back. This shouldn't make a difference, but I thought I would throw this out there. Barometric pressure is currently 30.01 in and the aquariums are at 420 ft above sea level.

Can't rule out sensor calibrations issues though so I will recalibrate again in a few days and see what the numbers look like

Yeah, >100% is definitely possible but with an air stone at <1 meter depth the steady state dissolved oxygen level should be no higher than 100%.

My tap water comes out of the tap at around 120% (and I'm sure it's not just oxygen but nitrogen and every other atmospheric gas). I did measure oxygen levels in my water change water storage barrel once. My usual process is to fill it with cold tap water, plug in a few heaters, add dechlorinator, plug in a circulation pump, loosely cover the barrel and wait for it to reach 75-78 F.

Even with all that I noticed it took about 24 hours to go down from 120% to 100%.

Since you recently filled the tanks they may be supersaturated in a similar fashion.

I would continue heating and aerating them and see if the oxygen levels decline to some steady state level that's ~100%.

Do you have fish in the tanks? If not, that's when I would acclimate the fish to the tanks.

You do need some oxygen demand otherwise there may not be significant differences in oxygenation methods.

 

I'll be doing a water change in 1-2 weeks. I would sometimes measure dissolved oxygen because I found that levels could get quite low quite quickly especially when water levels were low.

My plan is to water change like normal but wait and see if steady state oxygen levels can be achieved at various water depths. I normally refill in stages using a pump on a timer in the aforementioned barrel in the basement. I might be able to get some steady state oxygen levels vs. water depth data from this.

Several things could go wrong though. My fish panic when the water level is too low but usually settle down when it's >6" deep. Also, if the oxygen levels get too low I'll have to turn on the oxygen concentrator.

[Coronal Mass Ejection Carl]

Here are the dissolved oxygen levels from my water change when refilling. The three red arrows roughly represent when water was low (~6"), medium (11"), and high (~17").

I wasn't able to reach a steady state oxygen level for the low water condition since the fish had spazzed out earlier and were hyperventilating. They hadn't recovered after some time and knowing how fish sometimes die if they overexert themselves, I turned on the oxygen concentrator for a bit.

Edited December 24, 2020 by Coronal Mass Ejection Carl