If there is a magical trick I'd be delighted to hear it.
It's usually a combination of things I'd say. Physical cleaning does play a
very big part, whether by pole cleaning, heavy duty algae magnet, or
actually getting in there. Cleaning of one sort or another is probably the
dominant feature of the working day for most aquarists in Public Aquaria.
Water changes are also important to keep dissolved nutrients low, and with
freshwater these are easier and cheaper to do in volume than with marine
water (unless you are situated actually on the coast.
For large freshwater displays light intensity is often relatively quite low
which helps to limit algal growth.
Anywhere with a decent number of smaller freshwater displays often attracts
at least one dedicated passionate aquarist with a particular interest in
maintaining high quality displays of this type. This is very important. In
my view people will watch a well set up smaller freshwater display for at
least as long as they will watch some plump old Sand Tiger circling ad
infinitum (not knocking this species especially, you do need a 'pull' to
actually get people through the doors in order to tell them more about the
wonderful world of fish).
Biocontrols are always useful as well. It's amazing the amount of work a
healthy young pair of Ancistrus can save you, and even Apple snails have
Algae is rarely a problem in your average Malawian Mbuna display.
There are always the variables though. Take three displays at work, all
around the 1000 gall. mark. All with same water source and water change
routine, pretty much the same filtration and lighting (6500K MH). The one
that has the least problem with algae is by far the heaviest stocked one,
with the messiest fish (mixed Amazonian community) that get more food in one
day than either of the other two get in a week.
All have very low nitrate and phosphate because of the volume and frequency
of water changes, but the two lightly stocked aquaria each have varying
degrees of growth of filamentous algae and cyanobacteria.
With my own home display aquarium, a small South American display with some
rare and cute Dwarf Cichlids, I'm currently struggling with a hideous
cyanobacteria outbreak, whereas my play tanks here in my mini-office in full
sun for half the day have nothing more than a light growth of filamentous
algae. Same water, same foods, similar loading. The tank downstairs has a
filter system I built myself, these up here all just have cheap commercial
Sometimes you just have to scratch your head.
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