Note:Don't let anyone else tell you how much to add and expect that to be the right amount.
Just know what you add, go slow and measure as you go. Then for the next time, you know what to start with by going with a little less than initial batch, let that mix, then add to get to your desired salinity. I normally get myself to 1.021-1.023 in the first mix then go from there. I'm sure you know, but let some time pass between adding salt and measuring. I honestly let my initial mix go overnight. Then 30-45 minutes between adding and measuring the next day. My batch is not huge but I'm mixing 15-16 gallons per water change, only what I need and that's it. Also, are you using RODI? You may have problems down the road if you use tap (again you may already know this).
If you want to go by weight, measure yourself by creating your batch. That salt will come with instructions on how much to add per gallon to get a given salinity (via a measuring cup), tare the cup on the scale, then measure what you use to get your desired salinity. Sounds interesting if you have the scale, but I would simply do this myself. Have fun!
