  Using the SOAR 4.1 m telescope, we report on the discovery of low amplitude
pulsations for three stars previously reported as Not-Observed-to-Vary (NOV) by
Mukadam et al. (2004) and Mullally et al. (2005), which are inside the ZZ Ceti
instability strip. With the two pulsators discovered by Castanheira et al.
(2007), we have now found variability in a total of five stars previously
reported as NOVs. We also report the variability of eight new pulsating stars,
not previously observed, bringing the total number of known ZZ Ceti stars to
148. In addition, we lowered the detection limit for ten NOVs located near the
edges of the ZZ Ceti instability strip. Our results are consistent with a pure
mass dependent ZZ Ceti instability strip.
