Need help with skimmer

I am preparing to do some changes to my sump. I am actually going to add on to it. I have a classic 1500 otp reef octopus skimmer. I bought this unit from a friend who had used it for several years. It has a 3000 lph (750 gph) needle wheel pump. The skimmer is rated for 400 gallon aquariums. It works great! However, I am not sure I have the skimmer set in the correct depth of water. I have to restrict the flow into the skimmer to keep it from just pumping water out through the top where the collection cup is. Does anybody know how deep the water is supposed to be for these skimmers? Thanks in advance.

 

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Anybody know how deep I need to set the water in my sump for this skimmer?

 

I can't find any info on it but try 9" or 10" and from there you can make a stand out of eggcrate to raise the skimmer if you need to.

Hope that helps somewhat. :-/

 

Okay thanks