[adviner]

Under my stand i have a fuge (20 gal), i put acrylic on the top to cover the openings (except for the cutouts for the incoming, return pump and the electrical cables) so that it keeps the bubbles from going outside of the tank and less cleanup outside of the sump. But my question is, is that a bad idea? Should the sump be left completely open?

My tank on top just has the glass on it and a light, no hood at all.

Thanks

[BLKBRDTA]

If it's just the sump that is covered, then no it won't pose any problems down the road. As long as the refugium section has even a small amount of opening(s) somewhere, it will be sufficient enough to allow the gas exchange process to reoccur. Now a glass/acrylic top over the display is a different chapter of debate. I keep my display an open top, until leaving town for more than a couple days. At which time I use an acrylic sheet cut to fit the top of the tank, which as you probably know already, greatly decreases the amount of evaporation. But to answer your question, no the sump does not have to be completely open. It's more of a personal preference, than an avid technique.

[pogodzib]

No the sump does not need to be completely open, but the more open you have it, the better the gas and heat exchange will be so I recommend leaving the sump as open as possible.