1.) You do want to keep out as much dust, dirt, leaves, etc. as possible. In my greenhouse I am going to use nylon window screen over the shutter air intakes to minimize things coming in.

2.) Shade cloth and fans will go a long way along with large aquaria to minimize temperature shifts.

3.) Aluminum is bad.
http://www.advancedaquarist.com/issu...y2003/chem.htm