People with DO meters

[Randy Holmes-Farley]

That is interesting. THanks.

Unfortunately, I struck out finding a DO meter laying around.

[tatuvaaj]

Habib,

Thanks for the link !

edited: you don't happen to have anything about the pumping rate of sponges and tunicates vs. DO levels do you?

[Habib]

PO4 and tunicates I probably have but not sure aboutr DO will have a look.

[Greg Hiller]

>Unfortunately, I struck out finding a DO meter laying around<

Ha...not me!! Trouble is, most of our meters are intergral to the bioreactor monitors. I've been meaning to do this for quite some time. We commonly calibrate our DO probes for bioreactors in % of airsat. This calibration in a tank should be a easy, just take a small volume of tank water, kept at tank temp, and bubble the hell out of it for a few minutes, then set the meter at 100%.

Now...if I could just find an ICP to look for contaminants in my magnesium chloride ....hint...hint

Randy,

Are your pink skunks breeding?..on the tile?...I have rotifers coming out my ears. I was all set to raise my maroons, and the eggs fell off the tile for some strange reason.

[Randy Holmes-Farley]

No eggs on tiles yet.

[Habib]

Originally posted by Randy Holmes-Farley
One thing I'd like to test is how well O2 remains when I have a power failure and I'm left with just backup powerheads on a UPS.

Unfortunately, I struck out finding a DO meter laying around.

We have a O2 meter and pulling out some plugs is not that difficult.

If it has an effect then the very good suggestion of rsman should be tested. His idea and logic is extremely good and should be made known to as many reefers as possible.

BTW I'm just thinking uploud.

[rsman]

Im not a chemist and I think everyone knows it but just in case IM NOT A CHEMIST

when I was playing with a DO meter I was playing around with the ICRS that the people at Reed mariculture have nicely publicly given out. their first setup and my first setup both had some issues, in that you remove the rotifers from the culture water to filter them and at some points the oxygen sats would drop *Real low* like <5% killing things at that time I borrowed one (ok well stole with the intent to return and I did return it. ) and played around, a problem I noticed in the post by greg seemed to be that he was going to calibrate at 100% by airating SW, this doesnt work so well as you can pass 100% fairly easily. Trying to remember when I did this, it was probibly more than 2 years ago that I did most of this. I tested my reef, and the powerhead mentoned its a rio-180 it hides nicely at the top of the tank and the bubbles extend a good 3' away it was tested in real life when calf's grey davis droped the ball leaving lots of short poweroutages. the UPS its pluged into runs about $60 now and itll run for 24 hours no problems ive tested it by unpluging it a few times mostly just for kicks. because I was playing with my breeding setup (the ICRS) I am sure I made notes, but as it was on paper and ive got a good collection now about 7" stack, and Im very disorganized.

[Boomer]

I noticed in the post by greg seemed to be that he was going to calibrate at 100% by airating SW, this doesnt work so well as you can pass 100% fairly easily.



Yes, I would agree but there is more to it than that. First, one should not be trying to calibrate a DO meter, via aeration and assuming it is 100 %, it may be more or it may be less. Second on the link given and on the tests done by Samw and the links Samw gave all relate to limnological studies, the is the science of FW Ecology, not seawater but I guess that is Ok, at least you get an idea The meter he is using is a nice meter and does correct for salinity up 50 ppt so I would assume the values he gave are correct. As one can see, he is nowhere near 100 % sat., from his tests, par one brief reading. I have ways stated that one would be surprised at how low their DO really is in their reef tank. Many think they are 100 %. 100 % sat. of NSW @ STPS = 6.772 (mg/L) and FW is 8.39 (mg/L)

[Greg Hiller]

I'm sorry, I don't follow. You are saying that if I take a small volume of tank water (no critters in it), bubble room air into the water at tank temp and atmospheric pressure, and wait for the O2 level to come to equilibrium, I am not at 100% of air sat? This is 100% of air sat by definition seems to me. How can you 'pass' this number without using pressure, pure O2, or having some organism excreting O2?

FWIW, this is how (when we want to be particularly accurate) we calibrate our O2 probes in bioreactors. Have I been doing it wrong the last 15 years?

[Boomer]

Greg

How do you know it is not at 99 % or 105 %, when you calibrate ? When do you determine and how do you know when it is at equilbrium and it is 100 % ? Aren't you assuming ? You can mathamatically calculate sat.

http://www.thermidaire.on.ca/do.html

http://www.fivecreeks.org/monitor/do.html

Some things of interest

http://www.envirosim.com/products/bw...17_AirExam.php

http://web.njit.edu/~hsieh/ene670/oxygen.html

[Greg Hiller]

>How do you know it is not at 99 % or 105 %, when you calibrate ?<

Very simple. I put my probe into the water. Turn the monitor on. Wait 6 hours for the polarographic probe to become completely polarized. Do an electronic zero (highly accurate, I've tested with the zeroing gel, no point in using the zeroing gel) then dial up the probe to read 100%. Keep the air stone on for another hour to see if there is any drift. This is not rocket science! This is 100% of air sat by definition. Much easier and more accurate than doing calculations that make various assumptions.

I hooked the probe up to my main tank a few hours ago. I'll take a reading tonight before the lights go off, tomorrow before they go on, and maybe I'll stop the recirc pump for a few minutes and have the %$#% scared out of me by how fast the DO falls. I have a power head put in a position to suck in air when the water level drops if the recirc pump should fail, I'll check whether that keeps the DO up also. I'll also check to see whether my battery powered air pumps are up to the task. I once before in this tank lost several large fish when the recirc pump failed. The small fish all survived (save an Anthia, makes sense really).

[Randy Holmes-Farley]

Seems reasonable to me, although I've never actually used one.

[Boomer]

Greg

[Greg Hiller]

Well, I calibrated mine as mentioned above, and checked the calibration several times during the later measurements, little or no drift. Seemed to work okay. I measured the DO before the lights came on, about 92-95% of air sat. After the VHO's came on for an hour or so it was about 100%. After the MH's were on for a few hours it topped off at about 108% of air sat.

For an early morning reading, I shut off all the pumps in the tank and waited about 20 minutes (before lights were on), and I did not see much of a drop in DO, maybe a percent or two. With the pumps off I had to move the DO probe about in the water just a bit to get a good reading. Polarographic probes consume a small amount of O2 while they are functioning. Although I would have liked to get an idea as to how good my powerhead (aspirating when tank level drops after recirc pumps are turned off), and the battery backup airpumps worked, I did not want to leave the recirc pumps off any longer. Problem is many of the corals are exposed (grew to surface) to air when the recirc pump is off. Now that I think of it, I suppose I could have solved the problem by cutting off the overflow, and breaking the siphon on the return lines. Well, I need to get the probe back to work tomorrow. Perhaps I'll play again another day!

[Randy Holmes-Farley]

Interesting! Thanks for the info Greg.

[Boomer]

Greg

the water at tank temp and atmospheric pressure

I just noticed you did not mention Salinity. Are you correcting for that ? O2 meters have to be corrected for salinity also.

[Greg Hiller]

Boomer,

>the water at tank temp and atmospheric pressure<

81 F. Sealevel.

>I just noticed you did not mention Salinity. Are you correcting for that ? O2 meters have to be corrected for salinity also.<

No need to correct due to the way the calibration is performed. My tank is at about 1.024 at the moment.

[Boomer]

Well, I'm a little lost here Greg so I called both YSI and Orion. The really didn't agree with your procedure. I read the posted answers. One answer from them was you most certainly can go over 100 % by aeration, so how are you going to know where you are at, i.e., 102 %, 105 , 99 etc.. (Orion). The other, by YSI, they weren't sure if you were correct or not buy aerating a sample and stating it can not go over 100 %. My thoughts have always been that if you heavily aerate a sample of pure water, be it FW or SW, it can go over 100 %. Rsman mentioned the same thing (below). And salinity is still a factor. Ok, for one more phone call to WTW. Same answers, the meter must be corrected for salinity. I got the same answer form them on aeration. Aeration, is a form of increasing the pressure, so saturation can go above 100 % in pure seawater, in an open beaker, at sea level, @ 82 F. And that his is not a way to be calibrating a meter in seawater.

a problem I noticed in the post by Greg seemed to be that he was going to calibrate at 100% by aerating SW, this does not work so well as you can pass 100% fairly easily

[Habib]

Boom,

Yes, you never know how fast the oxygen in the water equilibrates with the current pressure of the gas phase.

However, IMO it still was at least a relative mesurement for O2 in which a certain point was set at 100%.


FWIW our probe can be calibrated using air and there is an adjustment on the meter when measuring saltwater.

[Randy Holmes-Farley]

If we are concerned about differences between 100 and 102% of saturation, then those sorts of differences can easily be accounted for by the pressure that bubbles are under when aerating a sample. Any bubble under the surface of the water is more than 1 atm, so the oxygen partial pressure can also be higher.

[Greg Hiller]

Well...guys...this is getting a little bit silly IMO. Okay, so the air stone was about 7 inches under the water surface. 33.9 feet of head of water is equal to 14.696 PSI (if you want to be exact, lol, of course I'm not including a compensation for the density of saltwater, lol). Anyhow, I will proceed with my slightly flawed calculation: Therefore, the increase in pressure over atmospheric is 7/12/33.9 times 14.696 = 0.252 psi. 14.696 + 0.252 = 14.94

14.94/14.696 = 1.017 OMG, you are right, I'm at 101.7 percent of air sat. LOL

Anyhow, I think the point of my measurements were not to debate the best way to calibrate a DO probe, but rather to see whether I was ABOVE air sat in my tank with the lights on, mid-way through the light cycle, and to see what the readings were like at night. At a reading of 108% (with the correction above ~110%) of air sat, I think my tank was clearly above air sat. Now, the question comes, why am I above air sat? I don't doubt that the skimmer on the system (ETS 700 with a strong pump) could push the DO above air sat on its own, if there was no consumption. Clearly however there is a significant amount of O2 being generated during the daylight portion of the light cycle, presumably by photosynthesis occuring in the tank.

FWIW, this system also has an additional tank(s) in the basement plumbed to it that is on the opposite light cycle. I would imagine that the differences in day to night DO levels in the main tank would be exacerbated if it were not for this additional tank.

[Boomer]

Greg

Anyhow, I think the point of my measurements were not to debate the best way to calibrate a DO probe, but rather to see whether I was ABOVE air sat in my tank with the lights on, mid-way through the light cycle

That is fine and I understand that. I don't think it was silly at all. I was just trying to get a better understanding of the issue and that was about it Thanks for the detailed answer.

Clearly however there is a significant amount of O2 being generated during the daylight portion of the light cycle, presumably by photosynthesis occuring in the tank

Yes, that is what I use to see also. At times you may see O2 bubbles attached to things, usually a sign of the water being over saturated..

Did you look at this post by Bryan ?

http://www.canreef.com/phpBB2/viewtopic.php?t=9942

[Greg Hiller]

I skimmed through the post, looks like that tank is pretty low in DO in the morning, it would make me nervous I think. My guess is no overflow has some impact, I didn't look to see what type of skimmer, etc he had.

[Boomer]

it would make me nervous I think



Yah, I thought the same thing. 50% is pushing it I could only imagine what would happen if the power or a pump went out

[Randy Holmes-Farley]

OMG, you are right

I made a lucky guess.

FWIW, I wasn't suggesting that I cared about a 2% difference.