I almost had a tank crash, well i guess you could call it that. I had glass lids on my 150g and did not realize what poor gas exchange could do. needless to say, my stable ph of 7.8 dropped dramatically, down in to the low 6's. I immediately pulled them off, added some surface agitation, and learned my lesson on that. Of course, i guess that's not really what kind of info/experience you're looking for?
"What, exactly, is the internet? Basically it is a global network exchanging digitized data in such a way that any computer, anywhere, that is equipped with a device called a 'modem', can make a noise like a duck choking on a kazoo." - Dave Barry