Sounds like MY experiences with DHL and UPS. To each his own I guess.
If you used copper algaecide "pre forum educated", then you still have copper in the water. I saw where you recently did a partial drain so hopefully the level is negligible. You might think about getting your water tested for copper just to be on the safe side.

Here's my theory on the foam, as I previously stated, I think it is leftover by products in the water. When you "shut the pump off and switch the valve back to the side jets" the combination of the pressure and air mixing with the water and "stuff" creates the foam. Do as I suggested in my previous post and let's see what, if anything changes. Try to bring your FC up to shock level before using the Polaris again.

Dave