I reccomend going with the standard glass tops. Acrylic / plexiglass will
bow and get distorted.

cover the water with. I have access to acrylic, or I can go buy
standard hinged glass tops. Are there any concerns with light filtering
if I use something besides glass? Also, how much space should I leave
for air exchange from the water? I was thinking of leaving the back 1

1"- 2" is a reasonable amount of space.