The only thing it can be is the water.
OK here is my suggestion.
You have IO so keep using that.
The water was cloudy before salt so we know it is a water issue.
Is this only DI water? if so the water may need to be filtered by RO membrane.
Those small DI filters Jakets mentioned are good but they only have a target of 60 gallons or so, and they cost 25 bucks and you still don't get
PURE water.
For the amount it costs you to buy water I would purchase a 5 stage RO/DI water system from
www.airwaterice.com (75 or 100 GPD) and they cost $149 which has a full size DI filter.
A couple of water changes and it has paid for it's self. This way you know it is pure. If you get the typhoon III it has a pressure gauge and comes with a TDS meter. Email Walter and tell me you are from 3reef and see if he will cut you a deal.
Have the LFS put a TDS meter in the DI water they sold you and see what that reads. I will bet it is high and they need to change the filter. But for $1 a gallon it will be cheaper and better to get a ro/di unit for yourself.
http://www.airwaterice.com/typhoon1.htm
The alk should be with in these ranges.
2.5 - 4 meq/L or 7 - 11 dKH or 125 - 200 ppm CaCO3 equivalents
Calcium:
380 – 450 ppm calcium ion or 950 - 1125 ppm CaCO3 equivalents