Is This Cyano?

[Ruth]

I think the real challenge is to find out where the nutrients that are fueling it are coming from in order to deal with it.
I have read that sometimes phosphates can build up over time in LR so you may want to pull out a rock, soak it in tank water swishing around really good and then test that water for phosphates. Same for the pellets, maybe soak in some tank water overnight (or while you are working that 12 hour shift) and then test that water. Also try taking a sample from really close to your sand bed, maybe after it has been stirred up a little. OTOH it could be that when you transferred everything enough PO4 was released into the system to fuel your small outbreak and it will be fine with continued water changes.