Are you using refractometer to measure the salinity?
Also, you should not pour the salt directly to the tank water. Dilute in the fresh water first, then pour in the tank.
Buying of expensives equipment means nothing if still don't know how to maintain the parameters right.
Also, should not depend on the LFS recommendation to buy this and that. Sadly to say, most of the 'advises' by them are wrong.