The plantguild PMDD mix, for example, has the potassium, magnesium, &
trace elements that can be made into pellets for the substrate. They
might also have a recipe for make potash pellets. Although they'd
probably recommend you buy one of their binding or extending powders.
I'm impressed at how brilliantly simple and inexpensive to hand
manufacture the Spot Fertilizing & power reactors seem to be. I'm
just starting with the power reactor, which is very efficient. I
don't know yet how effective or a PITA the fertilizer tool is. All I
know is I didn't want to waste the time trying to copy them. Using
them seems like enough of a PITA.

I guess by now it's moot but I checked another of my books. It says
Black Brush Algae belongs to the red algae group. It is carried in by
plants from Southeast Asia. It thrives in nitrate rich, hard,
alkaline water and with CO2 deficiency. It mainly attacks unhealthy
plants. It claims it is so tenacious that neither suction nor removal
by hand is possible without damaging plants. It recommends
Fertilization with iron & CO2, filtration through peat (to soften the
water & lower pH), replacing old fluorescent tubes & introducing algae
eaters.

So I wonder if your multiple aquaclears and hard, alkaline water are
partially to blame, along with a nutrient deficiency of these new
plants. I know you have taken steps to improve water chemistry &
supplementation. I guess adding driftwood to also alter chemistry is
not sufficient or desirable. Frankly I think DIY yeast CO2 is a PITA
& I agree that CO2 cylinders is prohibitive. I'd pick the brains of
someone over at plantguild for kicks. Even if you don't buy anything
from them, at least you have those Lilipon tabs. :-)