Any ideas why this problem exists....

Hi Everyone! It's been a while since I've been on but want to float this out there.... had pool built about 4 years ago... now it seems like the right half of spa is collecting more calcium than the rest of it. I've always thought there was an internal "problem" between the tile, grout and gunite wall... maybe its holding water, but no water loss to actually be called a leak. I've started descaling and noticed this area pictured which takes MUCH longer to dry out... about 20 minutes more! You can also see in the picture that the grout on the travertine is eroding and the wall in question has evidence of grout breakdown (opposite side not pictured) in areas that don't come in contact with water. Of course, the builder is non responsive since they've been paid.... so I'd like to figure this out on my own. I've monitored water level and no signs of leakage. Is my only recourse to regrout areas which come into contact with waterline? The location of water spot makes me think that tile above it may have a small gap at bottom, and water drainage is coming from there... since it would normally be below water line. Any advice on detection and repair? Thanks and Happy Father's Day to everyone out there!