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algae control (long, of course)

This is partly follow-up and partly new observations...

Last winter I posted a letter about my daughter's tank - a ten gallon tank
unfertilized except for fish food, lit with a single GE PL/AQ bulb on
about 18 hours/day plus some additional north light, UGF, low fish load
and water changes about 30% a month.  Its your basic beginner's setup. 
The tank was choked with hair algae that stubbornly returned immediately
after every cleaning.  I asked for ideas on how she could change things to
get rid of the hair algae.  My thanks to those who responded. 

What I did was have her reduce the light period from 18 hours/day to 12-14
hours/day and increase water changes to a weekly schedule.  The hair algae
growth immediately declined and at one point almost completely disappeared
- she didn't have to pull the stuff out every week.  More recently she's
been lax with the water changes and the hair algae is starting to

Another daughter, another tank, another algae problem...

My oldest daughter has for about 5 years kept a couple goldfish in a very
similar, beginner-tank setting.  This tank is in a shaded east window and
its hood doesn't produce as much light as the first tank.  Her tank has
always been plagued with attached brown algae - probably diatoms.  Early
last spring I gave her a large clump of java moss on some driftwood.  The
brown algae was completely gone in a couple weeks and the tank has
remained clear ever since.  The tank did get some drastic water changes at
one point when it was moved so we could put in some new flooring, but I
recall that the algae disappeared before that all happened. 

Yet another tank, yet more algae...

A couple months ago I built a new hood for my 38-gallon tank and replaced
the two old Chroma 50's with two new vitalites.  Between the improvements
in the hood and the new tubes, the light intensity jumped quite a lot. 
This tank gets potassium and chelated iron but is otherwise fertilized
only with fish food. 

Soon after the change in lighting I started getting heavy growths of beard
algae, which I treated by removing the effected leaves.  After a while the
tank (which gets no CO2 additions and is occupied mostly by slow-growing
plants) started looking pretty bare. 

Then about 3 weeks ago the tank developed green scum, which I skimmed
off, only to see it return.  Last weekend I transplanted five healthy,
straight-leaved val into the tank.  The pond scum started to regenerate
after the cleaning, then rather abruptly disappeared.  Also, I see very
little new growth of the beard algae. 

So what's going on here?

In the first case, the hair algae problem was probably caused by the long 
photoperiod and long period between water changes, and fixing those seems 
to control the problem.

The second case is much less clear-cut. The large mass of java fern could
have outcompeted the algae for some limiting nutrient, but the tank was
raggedly maintained and I imagine that the water was really a nutrient
soup.  The java fern is slow-growing, so I have to wonder how it could so
quickly reduce any nutrient to the point where the algae wouldn't live.  I
think the big water changes happened after algae disappeared, but
certainly that might have helped to keep the algae from returning.  Also,
the tank had drastic water changes before that didn't knock the algae

The last case is a little mysterious.  I doubt that five newly
transplanted vals could put up such immediate and large competition that
they could eliminate the green scum and curtail the beard algae growth in
just 4 days, even in a regularly maintained tank.

I recall reading in my wife's microbiology text that some protists (e.g.,
paramecia) are algae grazers and in some environments provide important
controls on algae growth.  It seems to me that growth and changes in the
population of these microscopic grazers could account for some of the
changes that we commonly get in algae populations during the setup of a
new tank and maybe some of the changes I described here. 

Both the clump of java fern in my daughter's tank and the vals in my tank
came from one of my tanks that has almost no visible algae.  Does it seem
possible that these plants could have carried a protist culture that 
expanded in their new tanks to control the algae there?  This seems like 
a plausible explanation for the decline in the attached diatoms and the 
green scum, but it doesn't seem to explain the reduced growth in the 
beard algae.  Are there other controls that might have cut in there?   

As always, seeking ideas.

Roger Miller