Carl,
boric acid can be used instead of borax to raise borate to 50 ppm and Proteam Supreme Plus achieves it's pH neutrality by being a mix of about 90% boric acid and 10% sodium tetraborate pentahydrate. Pure boric acid will slightly lower pH but, as we know, it will tend to rise on it's own so it is not really a major issue unless one adds it while the pH and TA are low and use a stabilized chlorine source, which will further lower pH. It's other drawback is that it is much more expensive than borax and muriatic acid. In reality, at normal pool pH range most of the borate in the water is in the form of boric acid with only a small percentage as borate ion.

Borate does a bit more than just fight algae. It also introduces a secondary pH buffer which is very useful with pools that have a SWCG or other form of aeration that tends to create pH rise from outgassing of CO2, which I consider to the the primary reason to add it to a pool.

Current price for a 50lb bag of boric acid from The Chemistry store is $81 + shipping so 20 mule team and muriatic acid is still the easiest on your wallet but a bit more work.