So I have dual dursos in a single center overflow section, and lately, it's been all-or-nothing in terms of which side is draining. I get little to nothing out of one side, and a torrent out of the other. That was not previously the case, but everything had slowed down due to obstructions and now that I've cleaned everything, I get almost all of the flow from just one side. The weirdest part is that it switches every now and then. I've been running filter socks, so since one side was doing all the draining I've just been running the one sock, but then randomly it switches to the other drain and bypasses the sock altogether. Very annoying Any ideas why it's doing this?