I am a newbie. My FOWLR is a little more then 2 mo. old. I added Instant Ocean directly to the water and cycled the salt in my tank for 3 weeks before adding live rock. Some of the salt never disolved and settled at the bottom of the tank. It was a small amount (but enough of a dusting to notice). After stirrring this undissolved white particulate it would imediately return. The water was *Never* cloudy though. I added 15 lbs of salt to a 54 gallon tank. I use well water which is Acidic, zero phosphate, zero nitrate, zero amonia. Alkalinity has not been tested for the tap water but is fine with seasoned water ( I do not remember the parameters of my test kit but this is where my alkalinity stands after adding salt).
I now mix enough salt to make 3 gallons of seasoned water at a time. I run a Maxijet 400 24/7 in this bucket with an areator and do a 3 gallon water change every week. There is always a little (? white salt) residue at the bottom of the bucket. The water is clear and not cloudy. The bucket is Orange so it is easy to see the undissovled particulate. In a white bucket it will probably go unoticed. I use a vented plastic spatula to help stir the salt.
I like the product and have not tried any other salt. Our local pet dealer ( who is in for the money so is an unreliable source) states that this little bit of left over residue is normal.
I am beggining to think the white granuals that do not dissolve are something other then salt and is a normal acceptable amount of unpure *particulate*. ( whatever is considered acceptable by the manufactures standards). I have not ever siphoned these particles out to examine under a microscope or see if I could get them to dissolve under heat.
Instant Ocean is a widely used product and hopefully someone will chime in to state whether a little bit of ? undissolved salt is normal for this particular brand.
Take care, Wayne