My hair is fine/low porosity. Baking soda makes it like straw. It hates even a little amount in anything.
If you have hard water and aren't doing something to remove the minerals, they are, at least, some part of your problem. There's a current thread on chelating that you could search to see what's being discussed.
My theory is that if you are truly low porosity, your rinse out is probably your least important product--it's not on your hair long enough to do much. It's your styling products that really matter. I use minute amounts of really rich products. My hair is frequently dry before the product absorbs (I use a curlease, CLU to scrunch, diffuse and air dry for several hours.)
My hair likes the more natural products. I try to stay away from chemicals, especially polyquats.
3a (Corkicelli), highlighted, fine, low porosity
modified CG, since April '07
CG since 3/11/08
HGs: Curly Kinks Satin Roots, Curlycue ReNew and Coil Jam; homemade FSG and okra gel; soap bars; DM MiraCurls Curling Gelly; UFD Curly Magic; Shescentit LIs; Sevi conditioners; Botanical Spirits Puree, CJ Repair Me