Ziggy - You are correct... It does change my SG
if I'm not watching my levels.
Usually I check it before I add the water with my Refractometer. Then based on that I adjust what I'm putting into the sump. IE: 5 Gal
mix being added would most likely only have half the salt needed. Like 2-3 gal
(In my case 2 1/2 scoops).
Plus. I'm lucky enough to have a small "leak" in the sump area around the hose coming off my skimmer. I just pull that salt off and toss into the next batch bucket.
Works out for me almost perfectly. I've nailed my SG
almost each week this way.