Ok, time for a top tip here. Adding salt and trying to mix it doesn't work because your allways waiting too long for the salt to disolve. This is why when you come back later on its allways higher than you expected.
These instructions are based arround a five gallon bucket.
Take 2/3rd's of a bucket of RO/DI
Mix in enough salt to make up nearly 5 gallons but a little less, my cup worked out at 4 cups to 5 gallons(ish)
so 2/3rd full bucket, 4 cups of salt and airate and curculate for couple of hours and youll have a bucket 2/3rds full or Hypersaline water.
Then de-salinate or Dilute untill the desired salinity is reached, youll find you can add water and test allmost straight away without waiting for the salt to melt. And youll also find when you come back to it later the salinity wont have bounced from undisolved particles gradually disolving.
Whatever you do, dont put salt in the bucket and then add water, youll make an exothermic binding reactory thingamy doobs thats no good for your salt or trace elements.
Cooks may see the similarity between this and mixing a cake, same deal.
I now use ocean water..so no more worries for me
except for unwanted pathogens, deseases, polution, contaminants, heavy metals, Hitchhikers, Algal spores, sewerage.........