Hi Marc,
<a href=showthread.php?s=&postid=14341271#post14341271 target=_blank>Originally posted</a> by melev
In the past (2003-2004), it seemed like all the SPS-diehards were aiming for 12-15 dKH, although RHF continually addressed that point, encouraging people to aim for NSW levels instead. That always made more sense to me.
Fair enough, but the recommended range here (8-11 dKH), which is the same as I see often recommnded, is still well in excess of NSW. Mean alkalinity in the mixed layer in the tropics is ~2.35 meq/L (= 6.6 dKH), and varies from ~6.1-6.9 dKH when you factor in regional variation in salinity.
Hence, 8-11 dKH is 21-67% higher than NSW levels. If such a large range, including 67% higher (11 dKH) is acceptable, why would 81% higher (12 dKH) or 97% higher (13 dKH) be a threshold to which or above which we dare not tread?
I don’t mean to be a bugger here, I’m just not sure this is a logical position for us to adopt
<a href=showthread.php?s=&postid=14341271#post14341271 target=_blank>Originally posted</a> by melev
The reason for the higher alk was that that, plus 6500K lighting, would result in very fast growth. The risk wasn't enough to derail that idea for many, which was that a precipitation event could occur. The tank would look like it was snowing in it, and alk & ca would bottom out quickly, leaving the hobbyist scrambling to get parameters back in line.
But the alkalinity is only part of what determines whether one gets a ‘whiting’ like that or not. Net abiotic precipitation of CaCO3, as aragonite, is possible when the aragonite saturation state (Omega-arag) rises above 1.0. In standard sea water (35 ppt, 25 C, 1 atm, total alk. = 2300 ueq/kg, [Ca++] = 10.28 mmol/kg, pHnist = 8.20) Omega-arag = 3.48. All else equal, Omega-arag increases linearly with an increase in alkalinity. An increase to 11 dKH yields Omega-arag = 5.90; an increase to 13 dKH yields Omega-arag = 7.00.
Whitings typically occur when Omega-arag is in the neighborhood of 15-30. We’d have to raise alkalinity quite high to produce a whiting under otherwise normal conditions. Usually it takes a large increase in pH to get to those conditions…or a massive overdose of calcium or alkalinity…or a combination.
For instance, to reach Omega-arag = 15.0 at 11 dKH we have to raise the pH to 8.855 (otherwise normal conditions). At 13 dKH we have to raise pH to 8.695 to get Omega-arag = 15.0â€"that’s a difference, but we have to raise pH way out of the normal range either way.
I suppose the difficulty I’m having is with the treatment of 11 or 12 dKH as a threshold. I don’t see any reason to do so. It may be preferable to shoot for a range of 8-11 dKH for practical reasons, but if 11 dKH is good, how can we reasonably say that 12 dKH is bad?
<a href=showthread.php?s=&postid=14341271#post14341271 target=_blank>Originally posted</a> by melev
I guess the best analogy is running your muscle car on the red line (RPMs) all the time, knowing you're running hot and running fast, hopefully long enough to win before your engine blew out.
Fair enough. I’d submit then, if we consider 2000-3000 RPMs fine and start to see all heck break loose in the neighborhood of 5000+ RPMs, does that make 3050-3100 RPMs necessarily that much cause for concern?
As I said, just picking your brain. Much appreciated
Chris
