Evaluations of this high pH statement?

[Fish E]

I was reading the "DSB in a bucket for nitrate control" thread and there was a post by Anthony Calfo addressing a question about the sand in the bucket fusing together:

"Aragonite only fuses when you allow your pH to drop low and usually rapidly as with misdosing supplements (too much kalk too fast, for example) or having unstable pH (dropping very low at night).

It is easy with good water quality/stability to avoid having aragonite fuse.

I'm so very strict about maintaining a strong and stable pH (8.3-8.6... never lower than 8.3 at night)... I have yet to have aragonite fuse. I recommend high and stable pH for more than a few good reasons aside from this issue."

What would be the advantages-other than preventing aragonite fusing (per Anthony), and the disadvantages-other than causing abiotic precipitation on equipment (per Randy's High pH:Causes and Cures article) of maintaining such pH levels?

[TheH]

I've read that aragonite fusing is thought to be related to high alkalinity, but nothing before about pH.

I guess he is assuming that low/high pH cycles sort of anneal the sand bed by partially dissolving it and then hardening it repeatedly?

8.3-8.6 sounds just a little high. I thought natural levels were in the 8.3-8.5 range?

[Randy Holmes-Farley]

There are several different issues here.

It is reasonably common to have sand harden, especially when new.

It is not entirely clear whether sand bed hardening is a purely physical process involving calcium carbonate deposition (or other minerals) that cements grains together, or whether it is mediated by bacterial processes, but it does not always happen.

It happens most frequently to new sand, and especially when the pH is high (as when using limewater). It happened to me when I first set up my first tank, but not when adding tanks to the existing system using the same type of sand. I would guess that higher alkalinity and calcium also contribute, as well as lower magnesium.

Often the effect disappears as tanks mature (the hard sections stay hard, but unclumped sand stays that way, and new sand won't as readily clump).
The addition of organisms (cucumbers, etc) seems to delay or stop the process as they keep it mixed up and perhaps break tiny links between grains before they become too established.



"Aragonite only fuses when you allow your pH to drop low and usually rapidly as with misdosing supplements (too much kalk too fast, for example) or having unstable pH (dropping very low at night).

Is that a typo? Was it meant to read "too high"?


As to advantages and disadvantages, the biggest advantage for many is that many calcifying organisms will calcify (grow faster) at higher pH. Higher at pH 8.3 than at pH 7.8 for example. :)

[Fish E]

"Aragonite only fuses when you allow your pH to drop low and usually rapidly as with misdosing supplements (too much kalk too fast, for example) or having unstable pH (dropping very low at night).

Is that a typo? Was it meant to read "too high"?



That quote was taken directly from post #158 in this thread: RDSB (http://reefcentral.com/forums/showthread.php?t=595109&page=7)

[Randy Holmes-Farley]

OK. Kind of a confusing statement from him relating rapid limewater addition and low pH, but IME, low pH is not a common driver for hard sand. :)

[Fish E]

Thanks for the comments and clarification!

[Randy Holmes-Farley]

You're welcome.

Happy reefing. :)