I am glad you got it figured out. I completely understand how frustrating and worrisome it can be trying to keep all of your water levels maintained.
I would recommend a auto-top off for evaporation if you don't already have one. A very handy little machine. I built mine but there are commerical ones available.
I use to have problem with water levels when I did my water changes. Now what I do is empty the auto top off bucket, fill it with the replacement water. I siphon out the water from the main tank and the auto-top dumps in the new water at the same time. I use the same size bucket so I can only remove the right amount a water. Once the water change is done, I rinse the top-off bucket and fill with clean water. This has worked very well for me. I don't have to turn off any of the pumps or valves so I don't need to re-balance the system.