Tea tree works pretty good, I use it as a pre-shampoo on my NANO days so I dont have to use but a little NANO.
I wouldnt expect it to completely control dandruff if you are getting flaking from using minoxidil. I had HORRIBLE flaking and itching on my first few weeks of minox5%. I was using Tgel, Tea Tree, Nizoral, Tsal, Head and Shoulders regular and Intensive care etc. There are many different "active ingredients" in various dandruff shampoos including coal tar, salycilic acid, selenium, zinc etc. You just need to find which one works best for you dandruff. Personally, I dont think Nizoral ever did anything for my dandruff since it only attacks from an antifungal perspective and my flaking was from scalp irritation. I still use nizoral because its beneficial for a male pattern baldness regimen.
The good news is that after about a month, my minoxidil irritation abated. I still get a little flaking from time to time but its very manageable and I get NO itching. I'm not sure if all the dandruff shampoos i'm using (Tsal/Nizoral, Tgel, Tea Tree etc all alternating) finally started kicking in or I just got used to the minoxidil. I think its mainly just cuz my scalp finally adjusted to the minoxidil
Hope this helps