Why does the level in my overflow change?

[laguest]

We have a 75 gallon tank with a 20 gallon sump. We installed the Eshopps medium overflow which is really great. The return pump is a Eheim Compact 5000. The tank has been running for approx. 6 months.

When we started we dialed in the pump so it would match the overflow, we had the water level in the overflow right at the top of the emergency pipe.
What keeps happening is when I do a water change I turn off the main pump. When I turn it back on it rarely goes back to the same level in the overflow. The water level is always low in the overflow. It never really seems to equalize, it's just low and make noise. I have been able to get it to correct itself by shutting the pump off and cleaning the screen. But I don think that is the problem, even when I do that most of the time it does not work.

It took a long time to dial in the relationship between the pump and the overflow, I really don't want to mess with the ball valve on the overflow or the pump output if I don't have to.

Anyone have an idea what can cause this?

Thanks

 

[Potatohead]

Pretty normal IME. Some people disagree but usually a Herbie fluctuates a little bit, depending on atmospheric pressure and other factors.

 

[henryle]

I have the eshopps 800gph overflow and it the water in the overflow box stays about the same every time I turn off and on the pump, it's not exact but about. If you increase the flow on your pump, it'll raise the level of the overflow box and will level itself out.


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[moondoggy4]

Mine used to do that but now I have a DC pump and they start real slow and start to build up and it helps settle within the overflow box. I think your pump is too powerful for your size tank. PS is it making a flushing sound?

 

[fermentedhiker]

I have to regularly adjust my ball valve. For me it's mostly stuff getting sucked into the pump intake and slowing the flow down. If I've adjusted it to be quiet at that flow rate when I clean things the pump flow rate goes back up to normal and then it overflows to the emergency drain a little. I have had occasions where a Nerite made it into the overflow but got hung up in the ball valve which caused the overflow level to increase until it was using the emergency pipe. Just had to open the ball valve all the way to get the snail to drop into the sump and readjust the ball valve.