Interested to hear your final conclusions in a few weeks time. Any effects seen with either treatment on shrimp at all?
The biggest being that after big water changes I'm spotting some with failing molts (WRoD), which was something I thought I had behind me. The 45 still has a few active planaria, guess I'll be treating it with Panacur soon. Your substrate thoughts seem likely. That tank has 4"+ of substrate. I'd have thought if it dissolved in water that it would get anywhere that's wet, but it's not looking that simple.