So last week I bought 5 gallons of premix salt water from lfs to change for my gf's nano. I used about 3 gallons on an 8 gallons nano. I didnt bother to check salinity of the store bought water because they are a reputable store and I have been using their water for almost 6 months now with issues. We then left for vacation and came back to a tank that is on the verge of crashing. I tested salinity of the tank and it is at 1.015 and then I tested the remaining 2 gallons of store bought water and it is at 1.012!!!! Luckily her fish didnt die but most softies are almost gone and the rbta is looking bad. I slowly raised salinity back up over the course of a few hours and a small water change. What should I/you do in this situation regarding the lfs?