Definitely check your specific gravity. You don't want to turn the tank brackish or into the Dead Sea either. Checking pH is also a good idea in case there's a big swing.
Are you using RODI
water? If not, you should to avoid algae problems. It's a good idea every now and again to double check the nitrates and phosphates of the new water to make sure it's clean going in. I'm sure a few folks on the boards can tell you about their RODI
filters wearing out and not realizing it until they were seeing problems in the tank.