Surfice scum

"Billy" writes:

Also I have read in books about Diatoms forming on rockwork what are
these.

Diatoms are a recently evolved form of phytoplankton (essentially:
small, floating food) that have silica based 'shells'. Most reefers
are introduced to diatoms as their first, "what in the hell is wrong
with my tank!" event. These diatoms show up as an ugly reddish-brown
bloom that can coat the rocks and sand. Once other microalgae
populations start effectively competing for food, this bloom is
naturally consumed or vacuumed away by the reefkeeper and diatoms
rarely become visible again.

Which is a shame, as diatoms are a fantastic natural food source for
your filter feeders, copepods, shrimp, snails, sea cucumbers and other
sand sifters. Another big benefit is that diatoms compete with blue
green algae (the same algae you're always scraping off the glass) for
food. Further, the presence of diatom growth makes the buildup on the
glass less aggressive and easier to remove. Finally, diatoms create
planktonic food (themselves) by consuming nitrate and phosphate (along
with silica) from the water column, helping most reefers in their
battle against dissolved nutrients.

The key to enjoying diatoms in a marine tank is moderation. When your
tank is new, everything is out of whack, and we shouldn't be suprised
that things take a while to settle into a stable system. Later, once
things have settled down and the tank has matured, diatoms can exist
in balance with other parts of the system, providing a valuable source
of food at the very bottom of the food chain without covering
everything in a reddish-brown layer.

I dose silica (dilute water glass) in my tank to maintain my test kit
at 1ppm. I also intentionally buy RO membranes that aren't very good
at rejecting silica (these are the "normal" membranes). The filter
makers are selling "premium" RO/DI systems that are removing stuff I
can use along with all of the stuff I can't. I'll just take the
normal RO/DI system and welcome the silica into my tank.

Since starting this dosing, I have seen two or three diatom "blushes"
where my sand will develop reddish shadows for a few days. Most of
the time, however, the only overt evidence of diatom presence is the
change of color and consistency of the gunk on the glass. Now it's
slightly yellowish, more transparent, and *much* easier to remove. My
clams are producing many more fully compressed fecal pellets, but I'm
not sophisticated enough to do more than guess that this is because
the diatoms are more digestible than other food they used to consume.

Here's a link to a reefs.org thread on the same subject (with some
links to some authors saying the same things diatoms):

http://reefs.org/phpBB2/viewtopic.php?p=447082#447082

Regards,
Ross

-- Ross Bagley http://rossbagley.com/rba
"Security is mostly a superstition. It does not exist in nature...
Life is either a daring adventure or nothing." -- Helen Keller