I have a pretty good sized one plumbed into my tank, but I have never used it as my tank has only been up for about a month. I don't want to kill anything off atthis point. Later on I am going to set it up on a timer and have it run for 2 hours a day. The flow is only gravity t'd off one of my returns, and it is controlled by a ball valve. I have heard that you don't really need them, but I think in the event of an emergency that will absolutely happen at some point, it is good to have them.
30L w/10gallon sump 4xt5ho; Up and running:125g long, 30g sump, 50g fuge.
"Life is tough, but it's tougher when you're stupid.”
John Wayne