Black root tips (pics)

I don't know if I should be concerned, two days ago my roots were only less than 1in. out of the baskets. Now the roots are a good 5 in. about 3 in. are submerged in my res.

Anyways, the root tips are a little darkened, I don't know what to think of this.

Sorry for the pics there not that great.

Wow, I found this thread on google. Type "Black root tips" and boom number 3. Wow, I don't know what to think about this.....