I haven't been on here in ages & I have the exact same problem as you so know that you are not alone. White gunky stuff under my nails right after shampooing
Similar to you, i've tried many an acv rinse, baking soda (this seemed to help the most) and scrubs.
I tried organic shampoos & everything & the only thing that helped was Head & Shoulders so right now I use it once a week. I wish I knew what the answer was.