He has some dry skin there and i want to brush him. what kind of toothbrush should i use, soft, medium or hard?

[Yoda]

As long as you aren't using toothpaste. He might even enjoy you scratching an itch he can't reach.

[Solipsist]

Start with Soft. You don't want to accidentally irritate his skin.

Use a clean (ie. new) brush and warm water. You could probably rub a tiny drop of almond or Vitamin E oil over the skin afterwards to facilitate healing and softening.

[marianparlors]

You can use it both where the power toothbrush heads alternates clockwise and counterclockwise rotation.

My turtle is fake, but this is what I had in mind