I'm confused. From the information you've given, 1) your current SS is clouding up in solution with your tap water. 2) It doesn't cloud when placed in solution with distilled water. These facts indicate that a change in your tap water is the culprit. Therefore, how is Five Star going to be able to answer the question of why it's clouding up? They have no access to your local tap water to conduct tests, even if they were so inclined. The local water utility might be a better source of information.
I have spoke with the water dept. and they have told me nothing has changed as far as their processing or mix ratio of river to well water. A river is constantly changing given runoff volumes and such, so one would expect that over the 4 years I have been using Starsan this behavior would have happened before.
An alternative explanation *COULD BE* something in Starsan has changed that reacts differently and becomes more cloudy when mixed with tap water with minerals. I am not saying that is the culprit but is a possibility.
I open the closed 2 gal bucket of Starsan I mixed this weekend. It was fairly clear but I could see several white "strands" suspended in the mix each about 1/4 to 1/2" long.
I took a PH reading and it came in at 2.1. It started at 1.9 as I mixed it a little strong at 1/2 oz to 2 gallons of cold water. I then stirred the solution and it became more cloudy and the PH dropped to 2.0. At first thought it looks like the Starsan didn't completely mix with the water and it was separating.
I am not sure this test reveals anything earth shattering and as long as the PH stays below 3.5 for a reasonable period of time I am not really complaining. I am experiencing a different behavior then I have before and would like to understand it.