Quaternions as Clifford algebra: confusion over grade

Question

If the quaternions are defined as the even grade multivectors in $Cl_{3,0}(\mathbb{R})$ then $i,j,k$ are all even. If they are defined as the Clifford algebra $Cl_{0,2}(\mathbb{R})$, then $i,j$ are odd grade, $k=ij$ is even grade. So in what sense is grade a well-defined concept, if isomorphisms do not preserve it? Or does this mean that the two definitions of quaternions are not truly isomorphic as Clifford algebras? (in the sense that $i\wedge j=0$ in the first, but $i\wedge j=k$ in the second) If so, is any one preferable?