Fishkeeping - Miscellaneous Algae questions

I've currently got BGA, Green Dust Algae and possibly Black spot Algae in my
planted tank. They're all pretty much under control (as long as I don't get
lazy), but the Green Dust Algae is the biggest PITA.

Questions:

1) Do Otos like GDA? I'm about to introduce some new Otos and I'm hoping
they will help,

2) The BGA seems restricted to the Hornwort. Does BGA only thrive at the
surface? The Hornwort has not been growing well at all since the BGA
arrived, is this a coincidence?

3) I'm not sure if I have Black Spot Algae or not. This originally showed up
on the Sword, but I thought it was some kind of rot from being lazy about
cleaning off the Algae. But now it only exists on the oldest leaves and the
new leaves are much more plentiful and clear of blemishes. I suspect it's my
increased diligence, but I can't rule out some kind of submerged leaf
syndrome or fungus. I've also got something similar on the Ludwigia, again
seems to occur on the most Algae ridden leaves. The GDA seems most plentiful
on the Ludwigia, but then again the leaves are red, so it's likely just more
obvious.