You could break up a puck and put the chunks over the spots.

I wouldn't advise ammonia products in a pool - PoolDoc or ChemGeek may be able to advise you better - I just don't have the depth or chemistry. I do know that you'd be likely to form chloramines and that monochloramine is an effective algaecide - is does stink and irritate skin. If you want to use the pool, I'd stick with shock FC levels and wear old swimsuits.