Return line question

[polarbear]

How do I keep the water from being sucked back into the refugium via the return line if the pump fails or the power goes out? I've read about drilling a hole on the top of the return line so that it breaks the sucken but will the water shoot out of there when the pump is on? Also I have a valve (not sure the name) that only allows the water to flow one way through it. Would this be a good thing to install?

[Mike M.]

The vent hole you drill should be on the bottom of the return line up in the tank. That way, the little pee stream of water is directed towards the tank. Should the return pump fail, it will back siphon until air is pulled through the very small hole which will then arrest the back siphon.

[Gonzobob]

Check valves are not recommended as they can fail. Drill the hole slightly below water level. You will have some drainback but this will break the suction and prevent any further drain.

[pbnj]

The output from my return line is in the top few inches of the display tank. Once the water drops below the output, the siphon is broken.

If you decide to drill a hole, it should be somewhere on the return line that is under water in the display tank (towards the very top).

[+dapettit]

+1 all the above.

[polarbear]

Thanks everyone. I'll drill it today about an inch below the water line.

[DaJMasta]

Just remember that 1 inch under means about an inch of your display tank WILL end up in the sump in the event of an outage - so be sure the sump has enough capacity. I prefer a pair of small holes near the water line. That way if one clogs (algae, snails, etc) you're still good and not too much of the display is siphoned into the sump.

[polarbear]

Cool I'll go just below the water line. Thanks.

[haitech]

what happens with the overflow?

[Timfish]

+1 and never ever use check valves or float valves on an aquarium, fresh or salt, they WILL fail.

[Timfish]

what happens with the overflow?

I'm guessing you're asking about the water draining over the overflow after the pump shuts off. If the return line opening is above the water line after the water drains down to the bottom edge of the overflow lip or "comb" a syphon hole is not needed (although I would still be inclined to drill one anyways). Almost always I see the return output below this waterline and water would keep syphoning until air was sucked into the return line and depending on the setup this can be a significant amount of water which may overflow the sump. The syphon hole needs to be cleaned regularly. Also, make sure the syphon hole is pointed down (didn't pay attention once and was very embarrassed when I turned on the pump ).