My deep six is spot on to my new refractometer. :|
I use instant ocean salt which is supposed to be a rapid desolving but it still took about 24hrs for the salanity to quit rising. I guess it needs to completely dissolve.
a piece of advice, take a min of 3 measurements for I've gotten some way out of whack readings before. You get 2 or 3 the same and call it good. Also be sure to wash it completely with freshwater after each use. The moisture left inside will evaporate leaving the salt which will drastically obscure the next readings.
I would also assume that alot of your salt fell to the sand before it was disolved. I premixed mine, poured it in an empty tank and still ended up with salt laying on the bottom.
I also find that circulating the water w/o a canister or HOB
type of filter, only prolongs the cloudiness. You're not allowing the particals to settle with the circulation.