rockys_pride;173251 said:
The reasoning behind the lower sg up here is for the oxygen content of the water. The theory reads that higher sg(1.026) water holds less oxygen than lower sg water(1.021). I don't have an ORP sensor to confirm, but I'm sure it would be an excellent science project for someone.
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It's definitely true that higher salinity yields lower oxygenation in the water. A good example of this is the "Dead Sea"...which is unable to support life due to it's high level of salinity and low oxygen content.
Concerning our tanks and the relative difference between maintaining one here vs. sea level...I definitely don't have the expertise to comment on whether or not a SG of 1.026 vs say 1.024 would really yield a noticeably lower oxygen content in the water given the same conditions apart from altitude. Considering the number of people that are able to maintain tanks at a SG of 1.026 at elevation...I'd guess any difference is negligible.
That being said, I
have actually researched a little in the past on altitude and oxygen content. I would venture to guess that maintaining an acceptable temperature and surface agitation is going to be more crucial in maintaining dissolved oxygen, and I wouldn't worry much about the salinity.
Here's a cool 3 dimensional chart that compares
dissolved oxygen vs.
temperature and
altitude. You can see that at lower temperatures (well beyond where we keep our reefs) altitude has a MUCH higher effect on dissolved oxygen content...where in comparison at temps in the range of 25 degrees Celcius, altitude has much less of an effect on O2 saturation. Although salinity isn't on the chart...if you were to keep salinity at a constant, acceptable level, altitude would have a minimal effect on your O2 content at the temps we keep our tanks.
Edit: I got curious and looked into this some more. The relationship between SG and oxygenation is non-linear...as SG increases it has a diminished effect on the dissolved oxygen content. So, although there's likely a huge difference between oxygenation of RO water vs our salt mix, the difference in dissolved oxygen between SG of 1.024 and 1.026 is much lower. Still looking for a chart/data on the subject, but inverse relationship likely looks similar to the one between O2 and temp in the chart I linked.
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