Odd observation - skimmer performance worse after adding outside air line...???

Replaced the piece am I holding in this picture with one that has a bigger nipple. It comes off the bottom of the pump motor.
I got it from reef octopus.

Note, it is actually the third one of those pieces I've had over the years. One of which was replaced because it fracking melted! Pic of the melt at bottom - not that it helps you, just thought it was interesting. Never ID'd why it melted. I replaced the part, same pump motor, never happened again...

 

That's exactly what I was talking about. That's essentially what I did to mine. I enlarged the hole very slightly and used a thinner walled nipple (end of ball point pen body).

 

Hmm... Will check on that with reef Octopus...

 

You do not need to modify anything. Bottom line, the venturi is designed for the flows you have and works fine. "IF" the tube is restricting flow, that isn't a venturi problem.

You have plenty of tube. It is larger and only 3 feet long. That isn't crazy.

There is no telling what other changes took place. Skimate color used to tell skimmer performance is like using paint color to judge car performance. Light skimate only has more water in it. Concentrating it does not equal "better" performance.

Simple solution offered. Take of the tube and see what happens.

PH changes water chemistry a lot. All other sorts of things could account for less organics.

The only way to tell air intake into a skimmer is to get a air meter. $30-$40 bucks. No point in guessing about stuff. Put a meter on it an find out. And if you are going to mod anything, you definitely should have one.

Cramming more air in does not automatically equal greater performance. Correcting a lowered air flow may.

And just for giggles... nothing "sucks" anything. High pressure flows to low pressure. Just sayin'

 

True...