Just go get the All Glass top, it comes with the plastic in the back that you can cut to fit exactly around your equipment, cuts evaporation down to a minimum. And the beneficial bacteria doesn't stay in the water colum, as stated before in this thread, it's in your gravel and decorations and whatever media your using. Don't vacuum your gravel during a cycle, I learned the hard way, or change your filter. If your filter gets clogged or dirty just rinse it off during a water change with the water you just removed from the tank. I suck my water into a bucket and then dunked the filter in the old water, removing any buildup of debris with my hand.