I've used and had great results from Oceanic and Tunze. Prefer Tunze and yes it is a bit more expensive but arn't the creatures we are keeping worth the extra $$$.
I've also heard of ESV B-Ionic Seawater mix being very good Current mixed numbers are (450 ppm Calcium • 3.25 meq/L Alkalinity • 1400 ppm Magnesium) and you can use it right away, no need to wait for 24-48 hours to use. This comes from a friend who is a good friend of Robert Stark.
Cheers,
Alex