Quick question: 1st PVC overflow

[888fish]

I've read through the MFK stickies, and done some YouTube research as well.

My specs:
- 168G freshwater glass tank.
- will replace all canisters with this DIY build. But leave in ugly sponge filter rated for 125g (connected to battery pumps) in case of power outage.
- planning to use 40g plexi tank as sump, with filter sock, ceramic rings, etc.
- planning to buy a 1200-1300 GPH rated submersible pump.

My 2 questions:

1. Should I build two PVC overflows? If yes, please state why, and what diameter PVC each?

2. If I don't need two overflows, what diameter PVC do I need for just one overflow?

Many thanks!


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[SickSauce]

I would like to know too

 

[888fish]

I believe from the MFK Chomper's charts that I need 1.25" diameter pvc to get approx 900 GPH. Buying a Quiet One 5000 pump rated for approx 1400 GPH with my tank height of 5" is the head loss, so the actual GPH is approx 1000 per their company's chart. With a ball valve set on the return plumbing, I should b ok. Will also add only the amount of water to my sump that will need exceed my tank total volume to prevent a possible flood. Will try with only one overflow first.

Someone with experience wanna chime in, please.


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