add another baffle after the skimmer that the water flows under then over the next then under to the return pump. same design that u have just one more baffle.
it depends on where the water outputs are at if they are down far in the tank it will drain until it gets air to break the siphon. that's why u need a hole drilled somewhere high. mine is in the elbow of the pluming where it enters the tank when the pump is on it has a little stream of water...
the best place to have a hole is close to the highest point of the return line. if you have a reef ready tank it would be inside the overflow near the top of the pluming to where it goes into the tank. the reason to fill the sump almost all the way is so that it gives you room. get it almost...
that's a big problem with test kits. many new and old are really not that accurate. they have done lab grade testing and use different test kits. old new and expired kits. some of the expired kits had closer results then some of the brand new kits.