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.
i personally prefer the open tank look on tall or bigger tanks EX, my 75 gallon tank rim sits 56.5" off the ground so i don't see the light reflecting into my eyes or guests eyes as they walk by. also my planted plus has been running strong on a open top with the water a little to low(splashing water on cover) for almost 8 months with no problem just wipe the cover dry every so often to keep water marks off of it.