CSS 65g leaking out of control valve.

Basically ive had this CSS 65g working great for a number of weeks. I get a large amount of dark tea colored water. However, just recently I decided to start filling my tank up higher to where the output of the skimmer is almost fully submerged. Last night and today it has been VERY SLOWLY leaking out of the top red control valve which adjusts how much the skimmer skims. Why is this happening?

 

There is an O-ring in there, shut it down and you can pull the knob out and and check that, if it's torn or anything you'll have to get a replacement

 

how would it get torn.....

 

anything could happen, salt creep getting in there, and as you turn it, could cause a rip, or a chunk getting taken out of it, i have same skimmer as you and ive had to replace that already as well, im not sure what the life span is on them but ive only been up and running for 8 months

 

Mine does the same thing if I have it turned up high.