Herbie overflow question

[XxSharkBaitXx]

Currently running a 30 gallon tank with HOB filter, upgrading to a 90 gallon tank with 30 gallon sump which I purchased used. The 90 gallon tank has a corner overflow with (1) hole drilled for a 3/4" pipe and (1) hole drilled for a
2" pipe. Will I be able to set up a Herbie over flow with this tank? The tank came with a Sedra 5000 return pump rated at 500gph.

If it is possible, what pipe would I use for main over flow and which for emergency.

[gunlocators]

I would think possibly but I am just learning the herbie setup myself. The emergency from my understanding would be the one drilled higher up but some experts here may chime in to let you know for sure

[hillscp]

I use the small pipe for my Herbie emergency but I don't think it is set in stone which to use. The important thing is that the main be big enough to handle the flow at full siphon and the emergency is able to handle the flow if the main gets clogged. At 500 gph I don't think you have a problem with either.

You can use this calculator to make sure. It will tell you how much flow a pipe can take given diameter and head hight.

http://www.beananimal.com/articles/hydraulics-for-the-aquarist.aspx

I love my Herbie. Tried a Durso and got bubbles and gurgling. didn't want to jump through hoops to fix it. I run 1200 GPH through mine (dual overflows).

HTH

Scott

Edit: make sure you click the "Submerged Discharge" radio button in the calculator. That's a Herbie or BA