refugium question

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Aquarium Advice Activist
Nov 16, 2003
San Francisco, Ca.
If in a refugium, like the cpr hob fuges, if the pump stops running will the suction of the inlet continue the vacuum and overflow the fuge? Or does it stop the suction?
Im debating getting the hang on back style fuge for a new 20 gal fowlr

Thanks, Brian
The flow should stop. Thats if the water level in the tank and the water level in the hang on fuge can come to an equilbrium level with out causing the hang on fuge to overfill.
Ok I was wrong this is how they work, the pump draws water into the fuge then siphoning gets it out. So heres a new question. If the powerhead stops working, will the water in the fuge drain out of the non operating powerhead? It seems that the water would drain out of the outlet, but that is in a seperate chamber and only that little bit would escape, but if the powerhead stoped working, would the fuge just drain into my tank until the fuge is almost empty?

Thanks , Brian
This is from the FAQ linked above.

Q. Why does the siphon break when the water level in the tank drops?

A. The outlet needs to remain completely submerged under the surface of the water in order to maintain the siphon. If the water level of the tank fluxuates, lower the outlet elbow on the AquaFugesm as low as it can go. If the water level drops below the outlet, follow the directions provided with the refugium to restart the siphon.


Above is a graphic from the FAQ aswell. If the pump that feeds the refuge stops then the water level in the fuge would lower till it was equil with the water level in the tank. As you can see above the return styphon will not break unless air enters the return tube and the only way this could happen is if the fuge was so high above the tank that the small return chamber in the fuge emptied or air entered the system on the tank size due to very low water. Nither should happen upon normal operation because water will stop moving once the water level in both systems is level.
So, youre saying it WILL come out of the inlet. If you look at that graphic there is wall separating the main chamber from the outlet chamber, so that would minimize the amount that drain back into the tank in case the pump stops working, right? But if it flows out of the inlet into the tank as well, then that would be a significant amount of water that would flow back in, especially if Im only using a 20 gallon aquarium. I guess I just dont get it. Maybe once I get the thing Ill shut the pump off and see if my tank overflows - which it probably wont, I just worry about everything.

Thanks, Brian
You will not need to worry about overflow. I have a cpr Bak Pak 2R skimmer which works in the same way. when the power goes out, the water stops pumping and empties through the outlet until water levels are even.
water stops pumping and empties through the outlet until water levels are even.

Thats the basis of the syphon principle. Water at different levels will try to find an equilbribum point. If the water level is always higher on one side then it will syphon water to the lower level. Once the water levels becomes equil then the water flow will stop until the water levels change. (ie. the pump starts back up)
I have a CPR hang on fuge. When you turn it off, it drains thru the outlet. if you drain the tank down further, water will drain through the inlet, which is why the inlet has a valve that you can close during maintenance so your fuge doesn't run too empty.
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