Questions about airstone's placement on dissolved oxygen

[James Croney]

Ive bought myself a 3-something gallon hexagon tank for my desk. I've got myself a nano usb airpump and neverclog airstone, and some other things from somewhere online to help complete the tank.

Id like to ask whether an airstone's vertical placement in the tank makes much of a difference for dissolved oxygen. I understand that some lesser amount of oxygen will not dissolve as air bubbles will travel less distance if the airstone is near the surface. My feeling is that "I want all the oxygens I can get omnomnom" but my curiosity has me considering how much I can get away with. If the difference is minor, I might be able to get away with a 'low flow' tank. This most likely would be terrible as the water volume grows, but for a 3 gallon even 2 inches under the surface is a large percent.

-- Besides curiosity, i have an accidentally rimless tank that i would love to grow duckweed as my tank lid. The guppies would love that too. The airstone being near the surface doesn't transfer as much force to disturb the water outwards. If the water surface moves too much duckweed gets  unhappy.  The tank is lightly planted with some guppy grass and some clay pellet substrate. Also has a wondershell in there.

Thanks for reading. 🙂

[Coronal Mass Ejection Carl]

It's not just the distance but the increased water pressure at depth.

I never officially tested it but when I did water changes and there was only a few inches of water the air stone didn't seem to work very well.

[ChemBob]

I believe the deeper air stone will cause more flow, also allowing the bubbles to disperse over a greater area of the surface. Everything I know says the more time the bubbles have in the water, the greater the oxygen uptake from those bubbles. The short duration the bubbles are in the water at the various standard aquarium depths like does not have a significant impact on the amount of oxygen dissolved. If I'm remembering my equations correctly, twice the duration in the water will allow for a little less than twice the oxygen absorption (I'm taking some assumptions on this, so it won't be perfect if you go digging and mathing). The additional water flow and surface agitation is likely another significant impact on dissolved oxygen. The flow allows better mixing throughout the aquarium and the surface agitation allows more exchange at the surface. Twice the surface area will allow twice the oxygen exchange at the surface. At 3 gallons, I think your assumption of an air stone just a few inches under the surface providing sufficient oxygen is good. Also, be prepared for more evaporation without a lif than with one, even if most of the surface is covered with floating plants. No idea how much floaters will help keep evaporation in, but I'm guessing not as good as a lid. 

[Daniel]

I will test today or tomorrow. It shouldn't take long to get some numbers on this. How much difference in depth do you want me to test for? I can easily do 10 inches, but it could be more if that is what you want.

[TheDukeAnumber1]

I don't have test data, but in my experience a little surface agitation is all you need to get sufficient oxygen into a 3 gallon. I wouldn't worry about its vertical placement.

[James Croney]

46 minutes ago, Daniel said:

I will test today or tomorrow. It shouldn't take long to get some numbers on this. How much difference in depth do you want me to test for? I can easily do 10 inches, but it could be more if that is what you want.

If you would be so kind... that would be awesome and save me a few hundred bucks on a DO meter. 😄

 

I have a nano usb airpump and a never clog airstone screwed in very tight. 

 

If you would test at "near the bottom" which is where I feel most people put it, and contrast those numbers to the stone being placed at about 1 inch under the surface, so that the top of the airstone is 1-inch below the surface.

 

I have attached an image of mine.

 

I feel like if the vertical placement "doesn't matter that much", then it opens up tank possibilities to people who want low flow or want to not disturb the water surface. I did try to neat trick I learned from a video with the plastic soda bottle cap to help divert some surface disturbance, but in a three gallon its almost like a lid. haha

 

 

[Daniel]

@James Croney I will set it up with a USB nano pump and a Ziss never clog airstone and test both bottom and 1 inch from top and let you know what kind of numbers I get.

[Coronal Mass Ejection Carl]

34 minutes ago, Daniel said:

@James Croney I will set it up with a USB nano pump and a Ziss never clog airstone and test both bottom and 1 inch from top and let you know what kind of numbers I get.

Is the tank reasonably heavily stocked? You'll probably need to have a fair amount of oxygen demand to be able to see the difference.

 

[Daniel]

I can set it any way people want. I could do a heavily stocked 10 gallon. Heck, I can run the experiment twice. Once with fish and once without.

[Daniel]

As per @Coronal Mass Ejection Carl's suggestion the dissolved oxygen sensor is placed in a heavily stocked 10 gallon aquarium:

• 20 zebra danios
• 4 adult swordtails
• 8 pygmy sunfish
• 1 pair Apistogramma nijsenni
• some unknown number of endlers

 

As per @James Croney a Ziss airstone on USB nano pump with airstone is currently placed at bottom of the aquarium.

If there are any other suggestions, tell me now before I start taking data.

[Maggie]

If it turns out you're not getting enough oxygen in the water, you could try a reducer valve on the air line, and tighten the air stone to make the bubbles as small as possible so everyone is happy. I have flosting plants (sprite, red root, and something-minimus), and they're all in a jumble, kept in the middle by a sponge filter w/airstone on one side, and HOB on the other. Its perfect as they never get whipped around! 

[Brandy]

I too have always heard that it was the surface agitation that was doing the O2 exchange, rather than the "bubbles" in the water. I have no idea how to test for that really. Everything I think of as a negative control seems far too involved/too much effort (eg. seal the entire surface of the water with an inch thick coating of oil--WITHOUT FISH!!). However, if you get no difference, that may be an explanation for why.

Edited November 24, 2020 by Brandy

[Coronal Mass Ejection Carl]

2 minutes ago, Brandy said:

I too have always heard that it was the surface agitation that was doing the O2 exchange, rather than the "bubbles" in the water. I have no idea how to test for that really. Everything I think of as a negative control seems far too involved/too much effort (eg. seal the entire surface of the water with an inch thick coating of oil). However, if you get no difference, that may be an explanation for why.

One thing that's already been done is to alternate between nitrogen and air and measure the difference in dissolved oxygen levels.

[Brandy]

3 minutes ago, Coronal Mass Ejection Carl said:

One thing that's already been done is to alternate between nitrogen and air and measure the difference in dissolved oxygen levels.

And? Link us nerds up! Is this a paper/journal article I can read? 🙂Also, that is a simple and elegant solution...which most home aquarists could not manage...I am not going to speculate on @Daniel's resources however, as he seems better equipped than my academic science lab at times!

Edited November 24, 2020 by Brandy

[James Croney]

@Coronal Mass Ejection CarlIt has 5 female guppies, soon to be 6 female and one male. Ramshorn snails and pest snails. Bunch of guppy grass and some small duckweed.  I do plan on having a "tank full of pretty guppies" on my desk so i do think the oxygen demand will get there sooner or later.

What has set me on this adventure, and well, what started me out was that I killed two guppies by not having an air stone in there. I tried maracyn for a while, but after some more reading it was clearly lack of oxygen. (top swimming, sporadic freakouts, and 'dizzy swimming') I thought it was an open enough environment to exchange naturally, and it wasn't. So off to some website online to get my nano airpump that I have been itching for an excuse to get.

I would think that the plants may have sucked out the oxygen, but either way, the fish seem much much happier with an airstone. It makes me wonder how the 'classic old school' fish bowls worked. I wonder if the shape of the tank being spherical helps water oxygenate. ... Not asking for a test on that one. 😉

[James Croney]

@Daniel That looks great to me. I would think that time of day and humidity as well as 'general atmospheric conditions'. So maybe don't take readings on a rainy day i would think.  After a reading DO with it at the bottom, move the stone to the top and take a reading once its had enough time to settle out. Maybe the same time next day? If no drop, next-next day? That would be my non-scientist take on it. 😉 If fish were not involved I would be curious to see how low it gets without an airstone and reset the data, but I have already proven to myself that is "too low" for fish so no need there. lol

 

Again, thank you for ... doing this. I didn't expect getting back validated data.  😄

[KBOzzie59]

@cory has a video on this.

 

 

[Daniel]

1 hour ago, James Croney said:

Again, thank you for ... doing this. I didn't expect getting back validated data.  😄

We will get measurements for sure, both signal and noise. Over the last few minutes I have thinking about what might fuzz up our data. Temperature could be confounding. The cooler the water is, the more oxygen that can dissolve in the water. Here is a chart from the last few days where the DO probe was just before I moved it.

It does not look like the DO is tracking temperature (at least lower temperature does not equal more oxygen, if anything it is the reverse).

I think what happens is when the lights are on the plants take in carbon dioxide and give off oxygen. The Amp_3 line on the graph represents how much power is being drawn, which is a proxy measurement for the lights.

So at the beginning of each light cycle, the pH and oxygen go up until the lights go off. And then when the lights go off, boom the plants start taking in oxygen and giving off carbon dioxide and both the pH and oxygen levels drop. And the temperature drops too because the lights provide a degree or two of warmth to the aquarium.

So you see why I am concerned about noise in the data.

 

[James Croney]

1 minute ago, KBOzzie59 said:

@cory has a video on this.

Oh man! how did i miss this? Ill watch in a bit when I'm not working. thanks!

[KBOzzie59]

Here's a nice USGS workup on DO.

 

http://www.usgs.gov//sites/all/themes/usgs_palladium/favicons/favicon.ico Dissolved Oxygen and Water

WWW.USGS.GOV

 

[KBOzzie59]

And if you wanna go full tilt Nerm!

World Water Monitoring Challenge Order Form

SECURE.LAMOTTE.COM

 

[Daniel]

I don't want to have to torture the data to get it to confess, so along those lines I just ordered a fresh batch of membranes for the DO probe that will arrive tomorrow. I will replace the current membrane and calibrate the probe so that whatever data we get the data will be of the best quality that can be efforted here.

[James Croney]

2 hours ago, Daniel said:

The cooler the water is, the more oxygen that can dissolve in the water. ... It does not look like the DO is tracking temperature (at least lower temperature does not equal more oxygen, if anything it is the reverse). ... I think what happens is when the lights are on the plants take in carbon dioxide and give off oxygen. The Amp_3 line on the graph represents how much power is being drawn, which is a proxy measurement for the lights. ... So at the beginning of each light cycle, the pH and oxygen go up until the lights go off. And then when the lights go off, boom the plants start taking in oxygen and giving off carbon dioxide and both the pH and oxygen levels drop. And the temperature drops too because the lights provide a degree or two of warmth to the aquarium.

So you see why I am concerned about noise in the data.

 

I see the concern yeah, but i think i have a way to make it happier.

I did understand that cooler water could hold more oxygen that heated water, and that is probably still the case. I agree that it appears to be the opposite, until the lighting is considered, as you said. Marker Amp_3 is a base for that cycle it seems, which leads me to think that leveling out the lighting would level out the warbles some. If you have a 60 watt bulb, perhaps a 30? I'm unsure of the negative impact of static lighting on fish... But my thinking is if you put in the overall same energy, it can't be too terrible. I have all my tanks outside... so no lights for them unless im working on stuff late lol

If I am wrong about the light leveling out, we may get into the plants/fish/tanks/microbes natural day/night cycles with or without lights. It would be very surprising to see if the tank 'sleeping' was the cause. haha

That, or I'm sure fancier math than I know could calculate the deviations given the Amp_3 marker.

Since we are a few shipping charges into this adventure, do you have any donation links that I should find? Yours or other places you would like to see a donation go to.

 

 

[Coronal Mass Ejection Carl]

 

3 hours ago, Brandy said:

And? Link us nerds up! Is this a paper/journal article I can read? 🙂Also, that is a simple and elegant solution...which most home aquarists could not manage...I am not going to speculate on @Daniel's resources however, as he seems better equipped than my academic science lab at times!

This is one of the earlier studies that attempted to quantify surface vs. bubble transfer in a bubble plume.

I do have a regulator intended for inert gases. I only need a metering valve, a flow meter, and a rented nitrogen tank and I can perform a similar experiment.

Click on the download button for the complete text:

http://digitalcommons.unl.edu//favicon.ico Gas Transfer in Diffused Bubble Plumes

DIGITALCOMMONS.UNL.EDU

---

The gas transfer in aeration systems is broken into two processes: gas transfer at the bubble interface and gas transfer at the water surface. Experiments were conducted to separate these two sources of dissolved...

 

[Coronal Mass Ejection Carl]

3 hours ago, Daniel said:

We will get measurements for sure, both signal and noise. Over the last few minutes I have thinking about what might fuzz up our data. Temperature could be confounding.

There's always something. When I was doing some informal water pump vs. wavemaker vs. air stone tests, I noticed dissolved oxygen was actually going down with the water pump (on the bottom of the tank moving water upwards). The extra current seemed to be making my fish expend more energy.