D-D H2Ocean Pro Plus Salt Mix. Question!!

Just purchased a bucket of this salt. Not following the mixing directions very well, can you guys who use this salt help me out. I mix my salt in a 25 gallon brute container and usually mix up 15 gallons at a time,was using instant ocean and would put 2 cups per 5 gallons and would get a salinity of 1.025 or very close to that. what are some ways you guys mix your H2o up. Sorry if this is a dumb question but any help would be very appreciated.

Thanks