Dissolved Oxygen Test Results

[Samw]

Originally Posted by teevee

I think you're right, but I'm a bit interested in how that would happen in the absence of any special method of induction. Interesting stuff anyways.

I don't know much more than what I could find on the net. I know its quite normal.

http://www.lander.edu/RSfox/415oxygenLec.html

"*values far in excess of 100% saturation are possible, even common

*on bright summer days photosynthesis produces oxygen faster than it can diffuse to the surface and escape


http://www.gvsu.edu/wri/education/manual/oxygen.htm

"Sunny days with lots of photosynthesis or turbulent water conditions can lead to supersaturation."

http://www.dnr.state.wi.us/org/water...der/oxygen.htm

"During daylight hours, it is not uncommon to find oxygen values in surface waters that exceed those listed in Table 5 (supersaturation), while at night or early morning before photosynthesis begins they may fall below those values."

Christy, no I don't have them in ppm. There's a switch on my meter I could toggle to get ppm readings for future tests.

[LostMind]

Extremely interesting SamW!

I guess you are not willing to remove your skimmers for a week and run tests?

[tatuvaaj]

SamW,

Someone posted a link to this thread in a thread I started at RC ( http://www.reefcentral.com/forums/sh...hreadid=382459 )
Interesting results, thanks!

I too would like to see results in ppm if at all possible.

[Samw]

Lostmind, I will test 1 night without the skimmer on.

Bev, I've recorded the oxygen % in the room's air. Before I go to sleep, it is 100.3%. When I woke up, it was 99.8%. LINK

I also tested the tank's DO this morning after I changed the airstone in 1 of the skimmers which allowed it to start collecting skimmate again. I dialed up the air output of my optima pump. I added new Kalk to my kalk dispensor. The DO reading this morning was 58.2%, PH was about 8.0. LINK

Sorry, I forget to measure in ppm again. Just for clarificiation, when DO in measure in percentage, temperature is accounted for. When measured in ppm, temperature is not accounted for. Right Christy?

Welcome to Canreef tatuvaaj. I'm hopeful that this thread will be useful to you.

[christyf5]

Originally Posted by Samw

Just for clarificiation, when DO in measure in percentage, temperature is accounted for. When measured in ppm, temperature is not accounted for. Right Christy?

As far as I know, temperature affects both percent saturation and ppm so it should be accounted for using both methods.

Christy

[Samw]

Hi Christy.

What I mean is that when we talk about DO as a saturation percentage, it is at a specific temperature. For example, 100% saturation at 20C is about 9ppm. However, 100% saturation at 25C is about 8ppm. So the percentage is always based on saturation at a specific temperature (and other factors. see below).

Measurements in PPM is absolute and isn't a function of temperature (although they do increase or decrease with temperature). 10ppm is simply 10ppm at any temperature. PPM is more useful as a measurement in some cases. For example, marine life require a certain ppm (different for each animal) to survive regardless of the temperature of the water. An animal that can tolerate wide temperatures but requires 6ppm to survive (for example) can survive at 60% DO at some temperature but die at 70% DO at higher temperatures because although the % saturation is higher, the absolute ppm is lower.

% saturation as a measurement is useful when you want to know how far off you are from ideal water quality. This link suggests that 100% is ideal.

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

I know for someone who deals with biology all the time (like yourself), all of this goes without saying but it is still worth pointing out to people who don't measure DO regularly. % saturation is basically a function of: DO (in ppm), temperature, atmospheric pressure, and altitude. Here's a good site with info on DO % saturation vs DO in ppm. Others can check out the 3 step equation to calculate DO % based on those function parameters. Its ugly.

http://wow.nrri.umn.edu/wow/under/pa...rs/oxygen.html

Here's the formula in Excel format:

=(($C$3*EXP(7.7117-1.31403*LN(B7+45.93)))*(1-EXP(11.8571-
(3840.7/(B7+273.15))-(216961/((B7+273.15)^2)))/$C$3)*(1-(0.000975-
(0.00001426*B7)+(0.00000006436*(B7^2)))*$C$3))/(1-EXP(11.8571-
(3840.7/(B7+273.15))-(216961/((B7+273.15)^2)))/$C$3)/(1-(0.000975-
(0.00001426*B7)+(0.00000006436*(B7^2))))

[Samw]

Ok, I've taken more readings since I cleaned up my airstone and increased the Optima Pump air output. I've included the ppm (mg/l) measurement in my last reading. It seems that the improved skimming added 10 percentage points to both min. readings and max. readings.


June 12
11:30am (Lights off)
67%, 28.1C, PH 7.87

June 13
12:00 pm (Lights off)
65.3%, 27.1C, PH 7.81

7:00 pm (After 7 hours of Full Lights)
119.9% (7.32 mg/l), 28.5C, PH 8.29