how do you keep air out of your cpr overflow

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Aquarium Advice Activist
Nov 17, 2004
Illinois USA
Hi All,
Just wondering I have 2 cpr overflows hooked up to 2 rio rejuvination pumps. It works beautifully except when the suck air out of the overflow c tube millions of micro bubbles get shot into the tank.

I've also read about using aqualifter vacuum pumps, but I've read that those require alot of maintenance and the lifespan isn't all that great.

Does anybody have any other methods of keeping air out of the overflow.
i have a maxijet in my sump that has a hose connected to the venturi. I use the pump to initially start the siphon and then i turn the pump off and the air just siphons out. In case the power goes out, i have a float switch that will turn off the main pump in case the water gets too high

yaksplat - Can you send us a small diagram on how you set this up? I really hate siphoning through the U tube during maintenance, and the fact that mine has bubbles too, which seems to create more noise. I also want to see how you setup the float switch so I can stop worrying about my tank over flowing. Thanks

Thanks for the quick reply yaksplat! So, to make sure I understand this correctly, you have a Maxijet in the sump and an airline tube running from the Maxijet to the overflow U tube to start the syphon? Once the siphon is created, then you turn the Maxijet off, right?
Do you also have a setup of your floatswitch and how it works? I just want to make sure that if I lose power and it comes back on, I don't want to flood the living room. Thanks again for your help!

worst case scenario right now, if the power goes out for more than about 30 seconds (the time it takes to siphon enough water out of the CPR, so that it fills with air and breaks the siphon), then the pump will cycle on and off as the water level increases and decreases as the float switch dictates.

Thanks Jim. How do you have the floatswitch configured? Is it drilled in the sump itself so it will know when to shut the pump off? I get confused with this part. Sorry.

The CPR siphon should never break because of power failure, regardless of how long the power goes out for. That is the purpose of the chambers on either side of the siphon. If yours drains out in 30 seconds, there is something wrong with it.

To answer the original question, I'm using a Rio 600RVT on my CPR. Yes, it shoots the air bubbles out whenever it finds some air in the siphon, but this happens rarely enough that it isn't a problem.

If...somehow... the siphon were to become completely drained, the Rio 600RVT would restart the siphon from dry before anything got out of control.

When you've stopped the system for maintenance the chambers drain down to a minimum. When you restart the system, the Rio starts to pull water out of siphon and can actually drain the siphon of water before the sump pump refills the tank enough to start feeding the siphon. This results in a lot of air bubbles shooting into the tank for a few minutes.

You can avoid the bubbles by leaving the Rio unplugged for a minute after you restart the system. This gives the sump return pump time to start filling up the tank and feeding the CPR. As I said, the siphon will restart without the Rio's help. After it has run for a moment or two, then start up the Rio and it will pull only a tiny bit of air.
well, that's the negative part of using a powerhead to clear the bubbles.

Salttanker - The floatswitch is mounted in the main tank. Your sump should be able to handle the water that siphons from the tank in a worst case scenario.

I really want to perform an emergency test of the system to see what it would do in case of a black out. I am usually at work for 8-10 hours, so chances are I wouldn't be at home if something were to go wrong. As a test, if I unplug the pump, the water will still run through the overflow until the chamber is empty, correct? Then, when I turn the pump on, it should fill the tank up like it was before without breaking the syphon? I just want to make sure I understand. Pre-drilled sure would have been easier. Thanks guys

yes, that is correct. But remember, water will still siphon through the return through your pump unless you have a check valve installed. Mine drains about an inch from the tank when this happens. I have a 1/8" hole drilled in the return pipe, right under the water line as a siphon break.

Exactly.....I'm trying to eliminate the micro air bubbles that the powerheads shoot out into the main tank. I was reading more and more about people placing the pump in the sump, but won't the micro bubbles just make their way to the main return pump and get shot into the main tank the same way, probably not as intense.

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