tank water level running 1/3 inch to high

[ducati1212]

I have a Red Sea 75 Gal Tank with a 18 Gal sump. I use a neptune apex and the ATK kit. I put the auto top off in the tank 2 years ago and have not really had to adjust it. I have a template made so I know its in the same spot if I need to take it out of sump and clean it which I do about twice a year.

Long story longer I have a mark on my tank to know where the water line is so when I do water changes I fill back up to the line and my tank about 2 weeks ago started running 1/3 inch higher. Visibly noticeable. So my water change this weekend I moved my atk lower in the sump 1/3 inch so the unit should kick on later and I thought fill the tank less. I filled back up to my normal fill line and within 2 days its back up 1/3 inch. I checked atk its lower in the water still.

What should I look at?? I guess my return pump could be pushing more water than my overflow is taking? Although my auto top off bin is using more water than normal so I think its that.

 

[Onewolf]

Have you ever cleaned your drain lines? Could be lots of gunk in them slowing down the drain?

 

[ducati1212]

I have not. what is the best way to go about that?

 

[Biokabe]

Check your drain lines, but also check the overflow combs. If you've had any stringy algae (hair algae, bryopsis, etc) become detached from the rocks, it can get caught on the combs and effectively raise the water level in your display tank.