# CPR overflow box for auto water changes?



## fish7days (Jul 30, 2005)

I was thinking of using an oveflow box, like one of the CPR models, as part of an auto water change system, by plumbing the outlet of the box through the wall to outside, and with a programmable timer have water flow into the tank via a solenoid valve. In theory the water that is let into the tank will displace water in the tank, and force it to flow out via the overflow box? I have no experience with overflow boxes and am slightly cautious as to the potential of flooding, such as when a possible sihon break may occur. I do not have a sump on this particular tank.

Any insight, help and tips will be much appreciated.

Thanks

André


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## MiamiAG (Jan 13, 2004)

Careful with the CPR overflow, it has a tendency to lose siphon.


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## fishfry (Apr 15, 2004)

The quote "play with fire and you will get burned" comes to mind, but in this case it is more like *"play with water and you will get flooded"* hehe.

The CPR overflows are great if you have no other option on a glass tank, and I recommend them the most of any hang on the back overflow, really quality construction. The key feature that distinguishes the CPR overflows from other brands is that they are "automatic restart", during normal use or a power outtage the overflow may buildup enough airbubbles at the top of the U tube to actually break the siphon. The CPR overflow has a nipple at the top that you attach to the venturi part of a powerhead and it sucks the air out and restarts the siphon automatically.

Some reasons not to use the overflow if you don't HAVE to:

1) The tank may overflow because water is being pumped into the tank faster than the overflow can restart.

2) The overflow's powerhead or airline hose can get jammed with algae or not start causing your tank to overflow.

If I was going to create an automatic water changer I would drill the back of the tank for a bulkhead and use an automatic ball valve on a timer. I would then install a float valve in the tank and hook that up to a hose that pumps water out of a resevoir. With the float valve you ensure that the pump never pumps too much water into the tank, but there is always the potential the float valve will get stuck in the on position.


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## fish7days (Jul 30, 2005)

Thanks Art,

Any other brand you would recommend?

Thx

André


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## fishfry (Apr 15, 2004)

CPR makes the best overflows because of the continuous overflow feature. Using one for about 4 years I think my tank only overflowed two times. Good luck.


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## MiamiAG (Jan 13, 2004)

I've heard plenty of horror stories with the CPR when the powerhead fails to remove the bubbles that are built up. Do a search on www.reefcentral.com on this.

I would recommend going with an overflow that uses the U tube. It maintains siphon without the need of a powerhead.


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## RTR (Oct 28, 2005)

I've had as many siphon breaks from U-tubes as from CPR-type units. For me, nothing equals monitoring the overflow. If it is opaque (my PVC DIY units), they are vented/bleed port fiited, so can just be coupled to a powerhead periodically (no lessthan weekly for me) to pull out any developing bubble.


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## fishfry (Apr 15, 2004)

Art_Giacosa said:


> I've heard plenty of horror stories with the CPR when the powerhead fails to remove the bubbles that are built up.


This only occurs on two occasions, if you never monitor the powerhead or you don't check the airline hose that connects to the powerhead to make sure it isn't clogged with algae.

Internal overflows are definitely way better than the cpr or any U-tube design.


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## fish7days (Jul 30, 2005)

I may have found something that will work. Remember, this is for a water changing system and will only be used when I add water to the tank. I do not have a sump.

I'll experiment with this http://www.aquarticles.com/articles/management/Krampetz_Automated_Water_Changing.html in a small tank in the garage, so if it overflows, no harm done....

I'll be in the fish box if I even remotely overflow in the house.....once.....

André


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## fish7days (Jul 30, 2005)

This seems to work pretty well. The feed side is outside the house, controlled by a solenoid and timer and inside I have a flow valve to set the amount of flow. The overflow is working flawlessly and I may even step it down to 0.5 inch as I change at a rate of only 5 gal per hour. When I mount it permanently, it will do a 50% water change for me every Saturday between 9am and 2pm.


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## RTR (Oct 28, 2005)

I use a lot of constant-level siphons, but when opaque as that is, I never go without an airline bleed port in the over-the edge pair of 90-degree elbows and an available powerhead to be sure the elbow is purged of air.


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