I'd suggested scrubbing the algae off, doing a water change, then adding some
plants. Elodea
does well, and I've heard hornwort will suck up those nitrates pretty well.

On another note. Snails will sometimes float on the water surface, I saw one of
mine
swimming in the middle of the tank, it was quite extraordinary seeing him using
his
internal body (pumping in and out) to move!