  We use a set of 45 simulated clusters with a wide mass range ($8\times
10^{13} < M_{500}~[$M$_{\odot}]~< 2\times 10^{15}$) to investigate the effect
of varying hydrodynamics flavours on cluster mass estimates. The cluster zooms
were simulated using the same cosmological models as the BAHAMAS and C-EAGLE
projects, leading to differences in both the hydrodynamic solvers and the
subgrid physics but still producing clusters which broadly match observations.
At the same mass resolution as BAHAMAS, for the most massive clusters ($M_{500}
> 10^{15}$ M$_{\odot}$), we find changes in the SPH method produce the greatest
differences in the final halo, while the subgrid models dominate at lower mass.
By calculating the mass of all of the clusters using different permutations of
the pressure, temperature and density profiles, created with either the true
simulated data or mock spectroscopic data, we find that the spectroscopic
temperature causes a bias in the hydrostatic mass estimates which increases
with the mass of the cluster, regardless of the SPH flavour used. For the most
massive clusters, the estimated mass of the cluster using spectroscopic density
and temperature profiles is found to be as low as 50 per cent of the true mass
compared to $\sim$ 90 per cent for low mass clusters. When including a
correction for non-thermal pressure, the spectroscopic hydrostatic mass
estimates are less biased on average and the mass dependence of the bias is
reduced, although the scatter in the measurements does increase.
