So it turns out you actually need to be kind of careful with MB7. After dealing with a cyano issue with an aggressive dosing of chemi-clean, I stepped up the use/change of GFO and started dosing the 'start up' dose of MB7 for high nutrient tanks, which in my tank worked out to about 70ml a day. I missed a couple of days to go up north over the holidays, but otherwise I was pretty religious about it, including turning off the skimmer.
I ran the inlet/outlet lines of the BP reactor in a bucket of salt water for the first 4 or 5 days after the chemiclean treatment while I started dosing the MB7 because I have no idea what chemiclean does to biopellets and I didn't want a bunch of excess organic carbon to flood my tank, potentially giving the cyano a leg up over the MB7. When I put the reactor back online with the tank, I put about half the daily dose of MB7 directly in to the pellet reactor to get things going again.
Now, I have to say I was extremely suspicious of MB7, and bacterial supplements in general. I've used them before and never saw an effect of any kind, and I've always been highly suspicious of aquarium supply company claims in general (they use as much pseudo-scientific non-sense speak as the alternative health industry), as well as being suspicious that a bacterial product could have anything living in it by the time you bought it at the store.
Well, I suppose the proof is in the pudding -
That disgusting pile of what looks like mucous is 1/4 of the goo that I had to eject from the outlet hose of my recirculating biopellet reactor yesterday. In less than two weeks of dosing large volumes of MB7, that outlet hose, which has remained clear and free flowing for nearly 2 years, clogged up so badly with that crap that water completely stopped flowing through the reactor. It's recirculating, so there was still some movement of water inside the reactor, but with the outlet blocked it slowed down enough that massive orange sized wads of white bacterial mulm had formed on the surface of the pellets that were largely stuck together.
The foam pads in my GFO reactor have also completely clogged up with bacterial mulm, causing the entire column, along with the foam pads, to rise all the way to the top of the reactor. Something that also, in nearly 2 years of running the tank, has never happened.
I've gone down to the daily maintenance dose of MB7, which if I'me measuring the volume of a 'drop' correctly, is about 6ml, so hopefully this stops happening.