about 1mm crushed coral.....4" DSB
. I've heard it can cause problems will the whole nitrate "spike" in the long run. but prior to the 2.5yr setup, the same tank was setup in my previous home for about 4 years.... with a 2.5" sand bed crushed coral, barely ever touched the sand stil never had a problem with it.
I've concluded that if your filtration setup is really good, you should never really have any problems.
So the 2.5yr setup, I went nuts on the filtration and put a 10ft sump and a few reactors... so far no problem, but still upgrading..., looking into a phosphate reactor and ozone reactor OR150 with reef octopus, then the filtration is complete