  Spin relaxation in a quantum Hall ferromagnet, where filling is $\nu=1, 1/3,
1/5,...$, can be considered in terms of spin wave annihilation/creation
processes. Hyperfine coupling with the nuclei of the GaAs matrix provides spin
non-conservation in the two-dimensional electron gas and determines spin
relaxation in the quantum Hall system. This mechanism competes with spin-orbit
coupling channels of spin-wave decay and can even dominate in a low-temperature
regime where $T$ is much smaller than the Zeeman gap. In this case the
spin-wave relaxation process occurs non-exponentially with time and does not
depend on the temperature. The competition of different relaxation channels
results in crossovers in the dominant mechanism, leading to non-monotonic
behavior of the characteristic relaxation time with the magnetic field. We
predict that the relaxation times should reach maxima at $B\simeq 18\,$T in the
$\nu=1$ Quantum Hall system and at $B\simeq 12\,$T for that of $\nu=1/3\,$. We
estimate these times as $\sim10\,-\,30\,\mu$s and $\sim2\,-\,5\,\mu$s,
respectively.
