If you had some major evaporation BEFORE you did a water change and replaced the evaporated water along with the water change, then you may see a spike in the SG
. It will depend on how much make-up water that you needed to put into the tank before the water change.
For instance if you needed five gallons of make-up water and took out ten gallons more for a water change, then you would have to put back in 15 gallons of saltwater. Since through eveaporation the salt doesn't go anywahere you in essence are adding more salt to the system.
I really shouldn't make that big of a difference but you can see if you do this on a regular basis you can raise your SG
everytime you do a water change.
Whatever I remove from my tank for a water change is all I put back in. I then top-off the tank with RO
water. This keeps it balanced.
125 Gal-35 Gal Wet/Dry-Tetra-Tec PF500 HOB
(3) AuquaClear 301 Powerheads-600 GPH
Automatic Tempature Controller
5-6 Inch Sand Bed-200+ lbs of LR