Just for testing. I figure, the new salt water will go in the chamber with the return pump and the old will be pulled out on the other end where the skimmer is. That way there's very little chance that new salt water will be removed right away.Outstanding work!
It looks like you're pulling old and pumping new into the same sump area. Was it set up this way just for testing and then you'll move the "pull" to a different area?