[Rig]

Why can't you run a tube from the top 1/2" or so of the tank down to a sump via a siphon, and then pump the water back, having a float switch turn off the pump if for some reason the siphon breaks? You could leave enough space in the sump so if the pump breaks, the top 1/2" or so of water could flow into the sump without a problem. Is there an issue with matching the flow rates?

I'm sorry if this is a really stupid question, but I'm not seeing the point behind the overflow boxes, like those made by cpr, when this seems possible, and much cheaper, cleaner, easier?

Thanks.

[dougc]

When the power goes off, the siphon will remove water from the tank until the water gets low enough to break the siphon. An overflow box prevents this because it stops draining water before the water gets low enough to break the siphon. If your idea was implemented, every power outage would result in a lost siphon.

A float switch wouldn't be a terrible thing in either case, since overflow boxes are not foolproof and can sometimes lose siphon during normal operation.

The best solution, of cours, is a reef-ready tank. There is no siphon. The only thing that can gum up the works is something crawling into and plugging the drain pipe. My drain pipes are screened to prevent that possibility.

[ricksreef]

plus trying to tune in a free flowing siphon to match the pumps
gph EXACTLY at all times is a little tricky.

[middlemark]

I'd agree with the above.
I think given enough time - it's very problematic.

And tuning tricky. Most PVC ball valves are hard to `fine-adjust' in my experience. My 40 is run with a Mag7 which can push more than the overflow can handle ... and with a valve even the smallest-seeming twist of the valve changes things a lot. I'd avoid it if you can find a way.

As someone who has come home to a `malfunctioning reef tank' a couple times [power loss, blown pump, overheat] ... while I've made it through without livestock losses or house damage ... I'm counting my blessings.

---
But, maybe I mis-understood your method somehow and it's not what I'm thinking.

[kevinpo]

I have done it before and have a customer that uses that method as well. Here are a few of the disadvantages of it.
You cannot get very much flow through them so you have to use multiple tubes (1" ones are best).
They grow algae in them which begins to raise the tank level.
You will need to have plenty of head space available in your sump for when the power stops and the return pump shuts off.
If you have a snail or hermit crab climbs up the tube your tank will overflow.
A small overflow box with the ends of the tubes in it works pretty well but you still have to keep the teeth of it clean and clean the algae out of the tubes often.

Regards,
Kevin