100% agreement with bingo
LifeReef external overflows are the best IMO.
Although a lot of folks use the CPR units, I prefer not to have to rely on a powerhead of any kind to maintain a siphon.
Powerheads fail as well at power up situations, especially the Rio600/800's - I've used them both.
I would imagine folks that have had bad luck with any external overflow losing it's siphon is either due to a flaw in it's original design, or undersizing their return pump.
If the overflow is designed right, but you do not have enough flow through the U Tube, it's easy for entrapped air bubbles to collect in the top radial curve of the U Tube, and eventually these air bubbles form one large bubble that will cause the siphon action to cease.
I've played around with various pumps and overflows, and have been able to reproduce this entrapped bubble effect several times. Not hard at all if you have too small a pump. You can see the bubbles form as the water rolls over the teeth of the inner box, and rise up into the U Tube. Eventually, the siphon breaks.
Here's a link to LifeReef.
Jeff makes 2 models only;
700 gph
1400 gph
They are a wonderful design, and worth every penny, but also make sure you have enough return pump to do the job as well.
The two go hand in hand.
<a href="http://www.lifereef.com/siphon.html" target="_blank">http://www.lifereef.com/siphon.html</a>
