  The complex dimension of the space of exactly marginal deformations for
quiver CFTs dual to IIB theory compactified on $Y^{p,q}$ is known to be
generically three. Simple general formulas already exist for two of the exactly
marginal directions in the space of couplings, one of which corresponds to the
sum of the (inverse squared of) gauge couplings, and the other to the
$\beta$-deformation. Here we identify the third exactly marginal direction,
which is dual to the modulus $\int B_{2}$ on the gravity side. This
identification leads to a relation between the field theory gauge couplings and
the vacuum expectation value of the gravity modulus that we further support by
a computation related to the chiral anomaly induced by added fractional branes.
We also present a simple algorithm for finding similar exactly marginal
directions in any CFT described by brane tiling, and demonstrate it for the
quiver CFTs dual to IIB theory compactified on $L^{1,5,2}$ and the Suspended
Pinch Point.
