If I could post photos I would, I have over 300 JPG files of groove images and all show carbonate in the bottom of the groove. so not sure what grooves you have looked at.
All I am doing is trying to remove some of the mystery behind LP cleaning and show more that getting clean LPs requires a bit of work if you are using VAC or US type cleaners, and can be done.
Have not tried the sink wash type cleaners so can't offer any insight on them.
If anyone wants to do a simple test, its quite easy. can be done on a vac machine (VPI or NG). use your favorite cleaning solution, apply it to LP. spread evenly across the LP surface. Let is sit for 10-15 min then vacuum off.
Go play the LP. you will notice a much quieter background.