Sand Algae

[PoolDoc]

Some years ago, I encountered a number of pools with unusual deposits that showed up in spring after I cleaned the slime off the pool walls. Close examination revealed tiny granular deposits, that looked exactly like glued on sand particles. But, on testing with acid, it turned out that all these sand particles were not quartz but were actually calcium carbonate capsules. Even more interesting, macro-photography revealed that live algae remained INSIDE of these capsules.

Apparently, some species or morphs of algae . . . or perhaps algal communities, since all bio-films comprise multiple species, and usually multiple kingdoms . . . produce these capsules. It's not clear whether they do so as a means of protection, or as a byproduct of extracting carbon dioxide from the water.

Anyhow, are my photos, from 2001 are first, followed by two recent photos from an AG pool owned by PoolForum user reddolphin. Reddolphin was able to confirm composition of her scale, by collecting small bits of the deposits, and putting them in vinegar, where they fizzed and dissolved rapidly. See RedDolphin's thread here: http://www.poolforum.com/pf2/showthread.php/11918

Because the calcium of these capsules is thin, they can be dissolved by low alkalinity water with moderately low pH. Essentially, the process for lowering alkalinity, here, will also remove these deposits. However, high chlorine levels are needed to bleach out the algal stains

The original slime area, under which the sand algae lay.
(The photo is upside down, with waterline tiles at the bottom.)


A partially cleaned area, covered by sheet-ed scale, rather than individual particles:


Sheet-ed scale on steps:


And, sand like deposits on an eyeball, with algae visible INSIDE of the capsules:


Again, the sand-like capsules:


A close-up of the capsules:



From reddolphin's pool -- you can see the individual capsules adjacent to some larger more sheetlike areas.
The area to the left is wet; the white more distinct areas are dry:


And, a slightly higher resolution shot from the same pool: