Buy a refractometer ($35-40 on amazon and more reliable/accurate then hydrometer)
Try to mix saltwater the night before if possible. I personally just mix it in the 5g buckets i have and then add it (never had an issue)
Buy a rodi
, at some point down the road, itll pay for itself in that the water it gives you is cheaper per gallon theb buying it from lfs
(check out bulk reef supply, they have units from 89.99 up depending on requirements.
When adding fish, always add the peaceful fish first, most aggressive last.