I don't have dandruff (at least I don't think so) but have very dry tiny flakes on my scalp (not itchy at all and anti-dandruff shampoos don't clear it) (like a fairly thick powdery accumulation of dry skin on my scalp plus my hair is also dry).
In the last 3.5 months, I've not used any hot tools (blow dryer, hair straightener etc.) on it at all, don't over-wash, use deep conditioner on the bottom half of my hair.
I've tried using shampoo in the past which made my hair like straw-dry even when applied to scalp only so I've just been using conditioner on the bottom half and nothing but warm water on my scalp (followed by a cold rinse sometimes).
I've always had a icky scalp so not sure what I can do :( I have very very thick hair too.