Been using IO since I started in reefing 3 years ago, I can't really say I've had any issues with inconsistency of levels. Maybe slight differences but nothing major. I keep hearing people say they roll the barrels, I can't see how that could help unless the barrel is not full to the top, otherwise I think it's a waste of time and effort with a full new barrel.
When mixing for a water change I always add the salt to the RO water as well. I check the mixture for temp, salinity, ca & alk before adding to my system. I tune up the mg level manually every water change, and my ca & alk are pump dosed.
