WOW! Thanks for the help! I have a light on for about 12 hours a day on that
side of the tank and no light on at all on the other half (it's a 55 gal tank
with two hood lamps). The light on side gets brown, the light off side is
fine. The light off side is next to a window, but we keep the shade closed as
the summer sun just bakes the tank water... We've never had any green algae at
all in this tank.

Our 10 gal tank with tiger barbs is always pretty green though - possibly due
to the plants in there. The two remaining goldfish (sadly down from the
original six of only two years ago) just go crazy on the plants. I had to even
remove the Pothos ivy and philodendrons. They completely ate all the roots and
were going for the leaves... Little herbivores... They do like their
zuccini...

We do use the tap water for both tanks, but I guess due to all the heavy rains
we've been getting, something extra that the diatoms like is getting included
in the source water... Also I had to remove the plants which gives a carte
blanche for the brownies' buffet.... Such a delicate balance...