James: I have found it possible to get no algae at all in tanks as small as 3 litres with no filter, no CO2 and no algae eaters.
The tank in the photo was 10 weeks old. It was initially planted with plants that were already growing submerged, which I think helped.
However, the most important thing, in my opinion, is to change 100% of the water every day just before you switch the lights on. All tanks where I have done this seem to be completely algae free after week 4.
Perhaps the combination of stable water conditions, water that is rich in CO2 and O2 and a little chlorine are bad for algae!