Water change days can be a PITA to get the same SG as the tank. The easiest thing to do is make sure both tank temps are the same. Go out and buy a digital meat thermometer if you don’t have one. It’s not important that’s it’s accurate, it just matters that you match the temp in the fresh and tank water. That way, when you measure using your refractometer, the new water is the same SG. If the temp is different, the Sg is different, causing swings. That should help with swings on WC day. Shoot for 1.025. Measure salinity twice a day if not 3 times if you can. Keep it stable. .025 will give you a buffer if it accidentally goes high or low.
Yep you rushed the corals a bit, but you can pull it off with good salinity management and upping your nutrients.
You got this!