Dissolved Oxygen data - Page 2 - The Planted Tank Forum
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post #16 of 20 (permalink) Old 09-15-2020, 12:57 AM
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Originally Posted by Mark Fisher View Post
O2 saturation at 79F is 8.1 ppm, and at 83F it is 7.8 ppm. Stress from hypoxia occurs at lower levels, ~3 ppm, not at saturation.
My temps run a few degrees below 79F, but my fish begin to struggle when I start to fall much below a crudely estimated 8ppm O2 due to the heavy CO2 concentration. So, I try to maintain the good gas exchange 24/7 to ensure full saturation in the 75-77 degree area. Of course, this reading is based upon a crude reagent test (Salifert), so I might have more room that I believe I have. I might be able to acclimate them, but I’ve bounced off of this ceiling many times while trying.

The fish don’t die, but are clearly stressed at these estimated levels and stress is not good long term.
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post #17 of 20 (permalink) Old 09-16-2020, 07:27 PM Thread Starter
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OK! Using the program associated with the sensor, I can only make the graph range consistent for Temperature (22C - 27C). Here are both graphs with Day 1 being the first one I reported with a large range in temperature due to house temperatures changing. Day 2 had the heater set to 77F/25C, so the temperature stayed more consistent.



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post #18 of 20 (permalink) Old 09-16-2020, 10:14 PM
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So, you've measured the tank having a ~4 oC point temp swing and with a ~1/2 oC point swing and DO readings appear to be unaffected, right? Wouldn't you expect at least a half-point compression from those DO extremes?

I remain interested in seeing how this turns out in terms of conclusions.
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post #19 of 20 (permalink) Old Yesterday, 01:44 AM Thread Starter
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So, you've measured the tank having a ~4 oC point temp swing and with a ~1/2 oC point swing and DO readings appear to be unaffected, right? Wouldn't you expect at least a half-point compression from those DO extremes?

I remain interested in seeing how this turns out in terms of conclusions.
I'm not going to make any scientific conclusions as I don't really have time to dive in and see if the data points are statistically different. The graphs appear to be very close to one another. The overall shape of the DO curves look almost identical.

My wife is an Ichthyology PhD student and she was interested in the idea that supersaturated O2 can harm fish. She found a paper from 1913 that said they did an experiment where they supersaturated water to about 400% Saturation and it showed no ill effects on the fish.
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post #20 of 20 (permalink) Old Yesterday, 01:55 AM
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My wife is an Ichthyology PhD student and she was interested in the idea that supersaturated O2 can harm fish. She found a paper from 1913 that said they did an experiment where they supersaturated water to about 400% Saturation and it showed no ill effects on the fish.
Look up "Gas Bubble Disease." It is similar to the "bends" in humans.

Here is a quote - legitimate or not - that I found in the first article that appeared:

"Other situations where supersaturation can occur include ponds with aquatic plant growth, because photosynthesis can increase the total dissolved gases. This is why aquarists recommend keeping keep pond oxygen levels below 125 percent."

A rapid temp increase can also cause supersaturation, although I don't know if 4 oC is enough.

It all points to a strong reason to ensure good gas exchange.
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