OK ~ if there is any doubt about the salt mix you use then listen up.
1. If it mixes cloudy and stays cloudy then don't use it.
2. When using a new bag, box, or bucket of any salt it is always a good idea to mix it up and then test it for calcium and alkalinity as well as magnesium if you have that test kit as well, before adding it to your tank.
3. If the magnesium is insufficiant then your water chemistry might not remain stable, that is your calcium and alkalinity may not stay in balance for long. Mg is what keeps the other two from doing the yo-yo affect. Mg also helps us to keep the other two up to the levels that we require for a reef.
All salt mixes can have inconsistancies to them no matter who makes them. It is always wise to test it before adding it. If I had done that, my tank back then might not have been nearly wiped out.
I've delt with Instant Ocean for years, and never got the results that I did with Oceanic salt. With IO salt and my tank it was always a constant battle of dosing this and dosing that. When I went to Oceanic my tank sprung to life, coralline came and stayed, corals responded positivly. I have used many salts, and I drip kalkwasser. so far best results for MY TANK have been with Oceanic.