Dissolved Oxygen Test Results

Samw · #1 06-07-2004, 08:19 AM

I've been running some tests with my new DO Meter and the results have been very interesting.

TANK DESC

38G tank containing SPS, LPS, softies, fish and many inverts. 2 airstone skimmers running but skimmers are not producing skimmate due to clogged airstones. 2 powerheads, 1 Aquaclear 200.

RESULTS

1. Morning readings before lights come on:

June 5
11:30 am
DO 52.6%, Temp 27.9C, PH 7.73

June 6
11:00 am
DO 57.7%, Temp 28.1C, PH 7.72

2. Readings with only 95W of Actinic VHO turned on at 11:00am June 6

2pm (+3H)
DO 64.5%, Temp 28.2C, PH 7.78

3pm (+4H)
DO 65.9%, Temp 28.3C, PH 7.78

4pm (+5H)
DO 66.6%, Temp 28.3C, PH 7.78

After 5 hours of VHO Actinic lighting, there is very little photosynthesis occuring in my tank (assuming the byproduct of photosynthesis is oxygen). The DO has stabilized at about 66% which is a slight increase from 57% when the lights were off.

3. Readings with VHO turned off at 4pm and 96W of PC 50/50 turned on at 4pm June 6:

5pm
DO 68.2%, Temp 28.4C, PH 7.80

6pm
DO 70.2%, Temp 28.5C, PH 7.82

7pm
DO 69.7%, Temp 28.5C, PH 7.81

With only 96W of PC 50/50 lighting, the DO has stablized at about 70%. Again, not a lot of photosynthesis is occuring.

4. Readings with PC turned off at 7pm and 250W HQI 10K turned on at 7pm June 6. Fan turned on:

8pm
DO 82.8%, temp 28.1C, PH 7.89

9pm
DO 87.5%, temp 27.9C, PH 7.99

10pm
DO 88.9%, temp 27.8C, PH 7.97

DO with MH lighting stablized at about 89%. There is now significant photosynthesis going on. DO increased from 57% to 89% with MH lighting.

5. Readings with VHO, PC, and MH turned on at 10pm (Fan on):

12am
DO 103.3%, temp 27.9C, PH 8.08

DO with all 3 lights turned on has jumped from 57% to 103.3%. This result is reproducible and has been replicated with similar results in previous tests that I performed on other nights.

Conclusions

The 95W Actinic and the 95W 50/50 PC did not induce significant levels of photosynthesis to contribute significant amounts of oxygen in my tank. Running a single 250W HQI MH bulb over my tank produced a significant amount of photosynthesis but was not enough to maximize photosynthesis in my tank during the day.

Night time DO levels were really low. Further tests will be developed to see if adding a normal skimmer can improve night time DO levels.

Beverly · #2 06-07-2004, 01:43 PM

Sam,

Interesting results. I am wondering if you had windows open at some point during the day that got closed partially or fully at night. With open windows, you will be getting a constant supply of O2 from outside that will get introduced into your tank by your PHs, airstones, AC 200. With closed or partially closed windows, the amount of O2 in the room available to go into your tank would be decreased.

Can you address the open/closed windows issue with regard to your experiment?

I have a 28g bowfront with 85w PC lighting and two Hagen 301 powerheads. I notice a significant amount of air bubbles on the macroalgae in that tank starting about midway through the day. MA in that tank is growing to beat the band. Windows are open all day and night now that it's spring. Don't have a DO meter to measure what's actually going on in the tank, though.

Samw · #3 06-07-2004, 07:54 PM

Hi Bev. No windows are opened in the room that houses the fishtank. The 1 difference between all of those readings is that the morning reading is taken after I wake up from my sleep so there will be added CO2 from me sleeping in the room. In the other readings, the room is empty of people. I would imagine my sleeping there would contribute a few percent but will be much less than 10%.

What I can do is measure the oxygen levels of the air in my room in the morning after I wake up and see how far off it is from 100%. If the measurement taken before I sleep and after I wake up are nearly the same, then we can conclude that the CO2 from me being in the room all night is not significant.

One other note is that my DE MH bulb is now 14 months old so a new bulb might give me better performance. I hope to switch over to a SE HQI bulb next using the same Icecap HQI ballast.

Doug · #4 06-07-2004, 08:46 PM

Does that tank have overflows. When experimenting with my 1 1/2in. overflows on my 225, I found a large ph difference between running sumpless or running the large overflows. Even with my skimmer & scrubber running direct from the tank.

That would be an interesting measure.

Samw · #5 06-07-2004, 09:10 PM

No overflows, sumpless.

Beverly · #6 06-07-2004, 09:11 PM

Quote:

Originally Posted by Samw

What I can do is measure the oxygen levels of the air in my room in the morning after I wake up and see how far off it is from 100%. If the measurement taken before I sleep and after I wake up are nearly the same, then we can conclude that the CO2 from me being in the room all night is not significant.

Sam,

I also noticed a consistently low pH in your results. Over the winter, we, too, had consistently low pH in our tanks. Did an experiment: once in the room where our tanks are, then once outside on our balcony:

- took a glass of NSW from the holding container, measured pH with a pH probe for 20 sec (or so, this was months ago now)
- left the pH probe in the glass, then added an airline with the pump on full. Measured pH after 15 minutes.

Results were that there was little change in pH in the room where the tanks were, something like .05. Outside, however, the pH change was huge, around 2.80

From then on, we always had a window or two cracked open just a bit, even on the most bitter of cold Alberta days and nights. We also added a fan to our hallway to circulate the fresh air. pH rose in our tanks, and our house felt less stuffy and fresher. At the time, I thought if I notice the difference in the air, the fish and corals must as well.