Thanks Brian, that's probably the most qualified answer! While my internal doesn't take up too much room, an external box would have worked better. Oh well, next tank :)

Even if both are considered reliable I'd choose an external (not HOB) overflow anyday. No holes drilled in the tank itself and it's strictly gravity without any reliance on a siphon. Even if both are safe I'd choose the external. Better with resale too since 99% of reefers would prefer a true overflow as opposed to a tank that's not 'reef-ready'.

LOL, thinking like this is how I ended up with 3 SW Sytems now,...Picking up number 4 this wkend so I can shut down two of them, the new one is also external overflow with some other niceties incorporated into the build.:biggrin:

This got a lot of replies, more then i could have hoped for. Thanks for the advice guys.

To get the true 'external' overflow, are they normally custom built?

I have had external overflow for almost 20 years...
The new ones are self priming...so if power go's off..they start atuomatically...
If this is your first tank...you will be moving up...usually a few times...this is where the external one pays for itself...I have seen a couple on here recently...one for 80 the other a 100.
They do not over syphon..overflow your tank...they work almost the same as a built in one....I speak from owning both....I still have my external one

Another one (CPR) for 65...

I just ordered an overflow box from Lifereef after I read this useful advise for not using a reefready tank.

http://www.aquacorals.com/ShopAquariums.htm

I have never used a hang-on overflow but if I did, I'd get a lifereef, and also add a float switch so my controller would turn off the return pump in the event of a siphon break.

Yes.

I've got the CPR CS 102 for since I started my tank 5 years ago. I've lost count on the number of aqualift pumps!

Each time the pump fails, I have the beginnings of an indoor pool in my basement.

I was told CPR makes on of the 'best' HOB overflows......they may but the weak point is Lee's Aqualift pump! Just flooded by basement again for the 8th time. The rubber diaframs all full of salt. If a standard siphon tube can run forever with NO air bubbles, why does the CPR require a aqualift pump to pull out the air?? Inherent design problem??

$1,000,000 question, is the aqualift used to correct a design flaw in the overflow?

I'm replacing mine with a Lifereef type using good old fashion siphon tubes!!