Need help with my tank water level

[Big Salty]

Hi everyone I have a huge problem I can't figure out. My tank level is asst the top and my overflow will not adjust the level in my tank. This happened once before and it was because the pre filter sponge was clogged and I no longer use it. I have a hang on the back overflow with no valve on it so the flow is wide open. My return pump is adjustable and I have it at the lowest setting and it's still at the top of the tank.again with no valve has anyone had this problem and if anyone can suggest anything that would be appreciated. I've had this overflow for about 5 months

 

[Lynn52]

Something is slowing the flow out of the overflow. Check your siphon. Over time the hang on overflows get air in them and lose their siphon, sometimes it just slows down. You can fix by restarting the Siphon. Another possibility is something like a snail is in the tubing obstructing flow.

 

[Waterjockey]

Something is slowing the flow out of the overflow. Check your siphon. Over time the hang on overflows get air in them and lose their siphon, sometimes it just slows down. You can fix by restarting the Siphon. Another possibility is something like a snail is in the tubing obstructing flow.

+1 siphon air bubbles