Expose rock/coral during water change?

[ErikH]

Also, I'm looking for a bigger sump, but have limitations related to cabinet doors.. What's the ideal sump volume for a 150? The answer is probably - the bigger the better, right?

Correct. The more water you have, the easier it is.... kinda.

[Dominican]

Right, more volume = more stability. 20g is pretty wimpy for a 150, but I've had it in one of those blue/grey rubbermaid tubs in case I have another "accident". Early in my adventure with this tank (my 1st, btw) I had the return too low, and a couple of power outages conditioned me to fear sump-floods. Since then I raised the return and should be ok, but I'm still a little paranoid. Need to upgrade to a bigger, nicer sump, and get rid of that rubbermaid...