Overflow
 

How reliable is overflow? planning to add a sump for my 90 gallon but i dont want to make any changes to my current setting. Any suggestion?

What do you mean by reliable? Do you mean will it stop flowing? Or do you mean will it overflow? What type of overflow are you considering for your tank? Internal, external, hang-on/syphon? I'm not entirely sure what you mean by you don't want to change your existing setting?

looking for a external hang-on overflow but not sure how well they work.

ah, I see. Sorry, I don't have any experience with those whatsoever.

http://www.lifereef.com/siphon.html
check this one out

Or you could build your own. I made this one and used it to connect a refugium to my sump. Worked very well. It has an airline hose at the top of the siphon connected to the input side of the return pump in the sump. That keeps micro bubbles from building up and breaking the siphon. It also provides for self priming and self starting if you have a power outage. I did a lot of testing with it too, and could not create a situation where it could fail or you could have a flood.
http://www.canreef.com/photopost/dat...edium/0031.JPG

More pics and reading on this type of design.
http://s868.beta.photobucket.com/use...embly.jpg.html

Thank for all the great suggestion. Need to do some testing before making any changes.

+1. I've been using the 1200gph lifereef for over a year. Not many power outages but I turn my return pump off to feed and its never missed a beat. They're big and pricey but if you don't want to or cant drill your tank, they're worth it.

Is the tank already on line or is it still in the building phase

I've use the same Lifereef overflow for the past 5 years on 2 different tanks. No problems at all. Starts and stops 100% without fail (so far) when I unplug my return pump.

The only time I ever had an issue was when a large hermit crab managed to get into the overflow box and plugged the tube trying to take a ride into my sump. My tank overflowed for awhile and when the hermit finally gave up and unplugged itself from the tube, the overflow simply went back to work. I came home to 4 gal of water on the floor, a hermit hanging out in my overflow box, and a perfectly running overflow!