[mike31154]

So there are two 'knobs' for flow control but you're still unable to dial it in reliably to prevent overflows? How exactly do these flow controls function(Edit: never mind, I see that there are two outlet lines each with a control, so this would be the same as the ball valve on my skimmer. Perhaps modifying the output lines to make them larger or having a single large line may help control)? Yes, very curious how it would work so well initially then suddenly get finicky. Clearly something changed for this to happen. A change in water level of the tank and/or any container that your skimmer pump may be drawing water from will often have a significant effect on the level in the skimmer itself. So a constant level in the tank is what you need to aim for. Auto top off for evaporation to keep things level. It's a bit difficult to tell how your pump is situated & where it draws the water from in your photo. Looks like there is quite an air gap between the tank rim & the water level at the corner of the tank where I assume the pump is. Some additional shots would be helpful to understand the set up. Definitely have a look at the pump itself. My little powerhead actually has a lever on the intake which allows for regulating output flow, but your pump may not be similarly equipped. Because mine is a small pump, I can leave the lever at the full open position & it won't overflow my skimmer. I'm able to regulate the water column in the skimmer with the ball valve on the return line. If I haven't cleaned out the skimmer box or the powerhead for a while, I need to start closing the ball valve to keep the water level at the sweet spot in the skimmer. The powerhead intake gets clogged with debris/algae & the output drops. I don't need to tweak the valve very often though & usually give the pump a good cleaning every water change which I generally perform every 21 days or so.