As Vaughn already suggested do a leak test, and fix the leaks. This will count for alot more than piddling with Glycerine, and it's only messy the first time, and considerably easier to clean up. You'll find that once the system balances correctly you'll have a lot of extra time on your hands to fritter away, and obsess little details like Water Changes, Pruning, and refilling that bloody bubble counter ! LOL. HTH Prof M