wow, amazing coral reef tank

love the colors.
sorry to hear about your problems with pellets.
could lowering of po4 too fast be the Issue with pellets ? what do you think ? I use Zeovit, and if the flow is too much, nutritions get processed too fast and corals seen to RTN prety fast ... from the base up, not sure if that was the case here though. maybe too much was used at first,
but Prodibio seems to be doing great for you so I doubt u would want to try pellets again
lastly, can we get a sump pic ? I enjoy sumps as much as I enjoy DTs lol