That product is cal-hypo. Cal-hypo in extreme amounts can do some funny things, but not foam up like that. Regardless, your water is sick and needs proper care. That starts with proper testing (at home). The free local testing is most certainly incorrect and so is their advice. You stated spending several $$$ already, and I'm sure they would love for you to come back.
Here at TFP it's all about simplicity.
Home testing with a proper test kit is step #1. After that, we help
you analyze those numbers and in your case, that would most certainly require the
SLAM Process. Depending on the products added to the water during your tenure with the pool store, a partial water exchange might also bee needed, but we'll know that for sure later.
For now, we highly encourage you to get a proper test kit - either a TF-100/Pro-Series kit (link in my signature) or a Taylor K-2006C. The TF-Series kits are a better value IMO, but you choose. Either way, you must have one. For the time being, I would do nothing to the water except add one gallon of liquid chlorine per day until you receive your kit. Then we can help you with specific advice based on YOUR testing.
YOU will be in control of the water, not some clerk at a local pool store.