For a tank cover would thin acrylic be better than glass?
Acrylic always ends up sagging.. flip it over and it sags again, brace it and it will sag less but inevitably sag again. Acrylic also clouds over time. The main benefit is, a cover will protect your bulbs. But they should be cleaned and wiped periodically anyway every 2 weeks or so. Again I find that no cover works best.