You guys are great. Thanks much. Such a simple question I hated to even ask, but glad I did.
Keep the level as Biz described. Just below the dividers. I have my float set just at the very top of them almost to the point of overflowing. You don't want it to overflow into each other so the skimmer and chambers work.
But you also want it as high as you can get it in the tank and center chamber. Sometimes if the level goes low in that center, you will get microbubbles from the return lines. Some of the 90 degree connectors don't fit tightly and they can suck air from the part thats uncovered with water.
If that happens, twist them tighter or put a layer of teflon tape around them.