Dissolved Oxygen Test Results

[Samw]

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.