Thanks Leigh..I very much appreciate your response.

Surface scum is not a huge issue for me, since I have a rather large canopy
that disguises it. But it would be nice to do something to limit it. Surface
current is probably the only way then.. Huh.

I am not concerned about CO2 loss, since I use a controller. In fact, I already
have three powerheads with low output, (~30 gph) to try to move the surface a
bit. (My tank is 135 gallons.) However, I may try a slightly more aggressive
flow. I am a bit worried, for the following reason.

Near my filter return, I tend to get blue-green algae every now and then. It
only appears near the filter return, and does not spread beyond that immediate
vicinity. I have come to believe that this may be due to my (low) nitrate
level and the fact that blue green algae can extract nitrogen from air. (What
is your perspective? Ever see this problem?) Now that I am actually testing
nitrates however, I am not so sure.. my nitrates seem to be smack dab in the
middle of the desirable range-- i.e., after a water change they are about 3
ppm, and toward the end of the week, they creep up to somewhere near 5 ppm.
Should I be shooting for somewhere near 10ppm?

At any rate, my worry is that if I put more surface current, maybe I will get
significant blue-green algae problems. What do you think?. Is there something
else going on here I am not picking up?

With my nitrate levels where they are, I am not intending to do much
supplementing. Right now, I believe potassium is my limiting nutrient. I am
adding more of that per week in addition to TMG (and have always added TMG).
If my nitrates sink really low with the addition of the extra potassium, then I
may supplement with nitrates. Sound like a decent approach?

Perhaps that will eliminate blue-green algae outbreaks all together. Does
anyone know if potassium shortage is linked to blue-green algae problems?

-Bruce