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NFC: Diatoms

Sorry I'm late with this one...but being something of an algae nerd, I 
couldn't resist this thread.

Kevin wrote:
>The above statements are making an assumption that you are dealing with 
>diatoms, which are often refered to as brown algae.  There are other algae 
>which are much less common which do have a brown shade.

Almost all "true" brown algae are marine.  There are very few freshwater 
species and they are relatively rare even in nature.  Brown algae of either 
water type tend to grow in cold waters...I mean really cold.  Stranger 
things have happened, but you probably have a much better chance of winning 
a $200 million lottery than of finding genuine brown algae in a tank.  Some 
green mat-type algae will have a brownish/golden appearance in areas, but 
green will also be evident.  In other words, I believe Kevin is correct in 
assuming diatoms infest Terry's tank.  I also agree that they are easy to 

A little diatom trivia for you:  Although diatoms are commonly (and 
mistakenly) referred to as brown algae, their closest relatives are golden 
algae.  The skeleton (cell walls) of a diatom is made of hydrated silica 
embedded in an organic matrix.  Each wall is composed of two halves that 
fit together like a shoe box and lid.  Some diatoms can move around by 
squirting stuff out of slits in their cell walls.  There are about 10,000 
known diatom species.  Sorry, I couldn't resist --- I warned you I was an 
algae nerd :)

The most common myth about diatoms is that they are caused by a certain 
light level (some say low, others high) or just old bulbs.  In my 
experience, diatoms grow in all light levels from low to high whether the 
bulb is old or not.  Diatoms, like all algae plagues, are invariably caused 
and sustained by excess nutrients in the water column.  As Kevin has 
already pointed out, silica is the most important of these in the case of 
diatoms.  However, removing silica, which can cost serious $$$, is not 
necessarily the best method for tackling diatom infestations.

IME, the two best solutions for diatom control are Otocinclus catfish or 
simply waiting them out.  A half-dozen healthy otos will clear a 
medium-sized tank (~55 gallon) in a few days and keep it clean 
after.  Waiting the diatoms out means scraping them from tank surfaces and 
letting the filter and water changes remove them from the water column 
which removes both the diatoms and consequently silica (and other consumed 
nutrients) from the tank water.  Eventually, the plague will peak and then 
fade away rather quickly.  For the impatient, there are silica removal 
resins that will take the silica out of water, but they can be a pain and 
are not cost effective.  Or you could use a reverse osmosis filter to 
remove practically all minerals from tap water, but RO can cause as many 
problems as it cures in some cases and it is certainly expensive both in 
time and money.

Terry, I wouldn't worry about diatoms too much especially since your tank 
is young.  They are common in the unstable environment of a new 
setup.  Just keep up on regular maintenance like you've been doing.  The 
diatoms will clear up eventually.  I'd go ahead and get some otos 
too.  They are one of the most useful fish in the hobby and few fish can 
keep up with them at removing mat-type algae.  I never have to wipe the 
glass, etc. in the tanks I keep them in.  They make excellent community 
tank residents too, but don't put them in with overly aggressive or larger 
meat-eating fish.  Otos are spunky but they're small.

I also recommend live plants for controlling algae, but that's a whole 
nuther can of worms (and a whole nuther email list ;).


Chuck Huffine
Knoxville, Tennessee  USA
mailto:grendel at usit_net