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Attack the blue-greens now, or wait?

I'm starting to get some blue-green algae in my first tank, a 10G which is
now two weeks old. Ammonia has peaked and is now immeasurable; nitrites are
on their way down (~5ppm); nitrates seem to be pretty low (but is hard to
tell with combo nitrite/nitrate Seachem test). I have read the archives and
Krib about factors influencing BGA growth, and decided that nobody knows
just what promotes good BGA growth.

My question is, should I go out and get some erythromycin now, and nip the
problem in the bud, or wait to see if it goes away as my tank stabilizes?
The first patches appeared on a Hygrophila difformis leaf; infection has
been pretty much limited to selected leaves of the hygro and the base of
the Laeliopsis (which are also surrounded by some brown hair algae at the
moment). I have removed the most infected hygro leaves. The plants were
given a ten-minute KMnO4 soak before planting.

I am fertilizing with PMDD made according to the Sears Conlin recipe,
except without the KNO3. (There is some nitrate in the mix because I made
my own trace element mix using Fe(NO3)3, and there is some extra potassium
because I neutralized the dibasic EDTA with KOH.) I also put a few pieces
of Jobe's Fern and Palm sticks (16-2-6). I am using a single 2-liter DIY
yeast CO2 reactor bubbling into a foam-covered powerhead intake. Lighting
is from a 2x40W Phillips Agrolite in a shop-lite fixture with the 20" tank
centered under it. Only fish are two Otocinclus, but there are a few
Daphnia in the tank as well. The plants are growing great, especially the
Ludwigia, which has already needed some pruning. I started with a 50/50 mix
of RO water and tap water; from what I know of our local water, this should
give 150ppm Ca+Mg as CaCO3, and a carbonate hardness of 65ppm. I intend to
gradually increase the proportion of RO water. My pH is hovering around
7.3-7.4. Substrate is a local 1-2 mm gravel which looks to be a
quartz-feldspar mix (decomposing granite and/or gneiss), plus ~100 g of a
local "laterite." The substrate was baked at 400+ F for about an hour
before placing in the tank.