CPR Overflow 1 vs 2?

[mrbee2828]

I'm working on my sump plans for my 75g SW build and was wondering about overflow and return placement. I was wondering if it would be better to do 2 smaller CPR overflows in opposite ends of the tank and returns in the middle pointing in opposite directions -or- should I do a larger centered CPR overflow and do returns on the outer corners. Thoughts?

I was also thinking about hooking up a SCWD with the dual overflows until the budget allowed for something more technical.

 

[tkeracer619]

CPR is designed to fail. Consider a LifeReef.

Use 1 overflow. With a HOB you need maximum flow through the device to get rid of bubbles. A CPR won't do that and needs an aqualifter to keep it going.

Either way snag an in tank ATO from autotopoff.com or similar and put this in your tank above normal operating level but under the rim of the tank. Plug your return pump into the ATO. If the overflow fails instead of a flood it will turn off your return pump. Saved my butt a few times with a customers trouble prone CPR.

 

[mrbee2828]

Why would having 2 overflow boxes limit the amount of flow going through one or the other? If the return can match it wouldn't they both be equal?

 

[tkeracer619]

You can probably balance them but I don't see a point. If you want more flow get a bigger overflow.

If you want more drains you might consider drilling the tank. It is the most reliable and cost effective solution. Drilling is easy but make sure the pane is not tempered.

 

[mrbee2828]

I was just wondering if grabbing more surface from different areas would be beneficial like a dual drilled tank with corner overflows.

 

[carey]

I kinda agree, if you want more flow just get a dual overflow. I have a CPR continuous overflow with dual inputs on my 125g. I've heard a few people say that same thing, that they are designed for failure, BUT I have never once had any issues with mine. I lose power all the time too and it just goes back to its job when the juice goes back on.

I'm only guessing now, but I think the dual overflows is valid in a large tank just because of the sheer size, probably easier to get more water into the sump. Just a guess though as I am not drilled on my big tank. lol

@tkeracer619- Whats the actual issue with the cpr, I've only heard they are bad from a few places and they never elaborated on why. I'm curious to see if there is a flaw in my setup.

 

[tkeracer619]

The design doesn't do a great job at removing air from the siphon. Too much internal volume on the siphon so flow is low vs a utube style overflow that moves the same amount through a much smaller space.

A utube isn't necessarily the answer. About the only one I can recommend is a lifereef but if it is working for you I would just keep doing what your doing.

As long as your skimming the proteins off the surface of the water the extra linear inches on a dual overflow won't really provide any benefits over a single overflow. In fact a lot of people who have taken it one step further for a coast to coast overflow often have to use power heads to push the proteins over since there is less water flow. The height difference between the water and bottom of the teeth pulls in the proteins.