atmospheric pressure?

[panther]

I've been lurking around here for a few weeks now, and one question that has come to my mind deals with the effects of atmospheric pressure.
I haven't found any discussion on this in either books or any BBs. I live in Mile High (Denver) and wonder how the thin air here would affect things if at all. I would imagine that it might have some effect, but have no idea what it could be. Any thoughts?
On a side note, I've visited almost every lfs here and every single one of them use bio-balls for their biological filtration. The general consensus here is that such filters can become nitrate factories, and that seems to make good sense. The one reason only a couple of the lfs have given me is that they give excellent aeration for Oxygen replenishment. Could that have anything to do with our thin air and low atmospheric pressure up here? Perhaps with lower a.p. the water is not as easily oxygenated? Just a thought

 

[riddlebum]

I've learned in my fluid mechanics class that when measuring the pressure exerted at a certain depth, you can pretty much ignore gasses. So i would assume the pressure on your tank is about the same at sea level then at your altitude.

 

[mithrax]

I think the percentage of O2 is constant regardless of the altitude (Correct me if I'm wrong). If that's the case, O2 diffusion of water is not different at sea level. Somebody get their Physics 101 textbook, quick!

 

[broomer5]

For what it's worth ....
Mithrax is correct - the percent of oxygen in relation to nitrogen and other gases in the atmosphere is more or less constant at various altitues ( more or less ). At higher altitudes there is just less ( fewer molecules ) of O2 present, compared to the O2 levels at sea level. The air is less dense in Denver Colorado than Miami Florida.
The pressure in your tank is more influenced by the specific gravity, but is affected by altitude and gravity as well .. slightly.
A column of freshwater ( tank ) 20" high with S.G. 1.0 would exert about .72 psig at bottom of tank at sealevel.
A column of saltwater ( tank ) 20" high with S.G. 1.024 would exert about .74 psig at bottom of tank at sealevel.
Hardley worth the trouble of doing the math.
Gravity would come into play only at great altitudes, at farther distances out in the Earths atmosphere.
The farther you go up, eventually the weight of the water decreases, an so the pressure.
Again - not worth worrying about unless you are planning on setting up at salt tank in orbit.
Without getting too in depth with the gas laws, Boyles, Charles, Daltons and Henry's, partial pressures, vapor pressures and such .... suffice it to say that there would generally be less O2 gas ( and all other gases ) available at higher altitudes, and less gas available for exchange in the water, until the O2 saturation point is reached. Once saturated with O2 gas the water can basically hold no more. I'm not sure if water in Denver can hold more O2 gas than water in Miami - maybe someone else here can answer that.
I suppose it's possible that your LFS's use wet dry's for additional O2 gas exchange, but I imagine there are some Denver hobbiest's that have sucessful tanks with out them.
If you see a blue flame angel - call 911 and start administering oxygen.
[ June 05, 2001: Message edited by: broomer5 ]

 

[panther]

Some great responses! Definitely put a smile on my face broomer5 I'll keep an eye out for any blue flame angels.
I kind of thought the difference might be less than noteworthy, but thought I'd ask anyway just in case there was something I hadn't considered.

 

[nacl-h2o]

Many LFS use bio-balls at the store because of the constantly changing bio-load and frequency with which they over load the tanks. The systems using bio-balls are also cheaper and use less space than using LR. Many of those same people who use bio-balls in there stores use LR at home.