Finnex Warranty RequestsOpen top is great. I agree with one less thing to clean. However, open top will allow moisture to wick into your light fixture and void the warranty if the light goes down. This is especially true if you run airstones or the filter output to ripple the surface. A tiny micro bubble is harmless when it pops, but 25 billion of them popping over time will eventually take its' toll. If you are past the warranty period then the above link is irrelevant but you will still face a replacement in the future sometime. Water makes mountains into boulders, boulders into rocks, rocks into pebbles, pebbles into sand, etc. It will also mank up the surface mount components on your light fixture. A few other things about the canopy, it helps with temperature control, keeps evaporation down, keeps jumpers in the tank, and probably helps with the control of airborne nuisances. Just my 2 bits worth, since 2 cents is worthless nowadays.