I've never used water based poly, but everything I've read says it can only be thinned with water.
Mineral Spirits (what we call Mineral Turpentine) is used for thinning oil based products. It certainly looks like it worked, but I'm curious how.
It doesn't seem possible from a chemistry view. (However, I am not a chemist)
Making the world a better place; one guitar at a time...
I had seen many videos of how to make home-made wipe-on poly, and I notice just now that mine is water-based and should not work with mineral spirits. But in the end it blended well and I am happy with the result, so the consequences are not dramatic.
I am refinishing the back (I sanded it back yesterday because of clamping marks, although I thought I was careful). I will try this time to thin the poly with water and see if it works differently for me.