Hopefully the grouper doesn't turn into a terror. They are awesome fish.
I took biopellets offline about a month ago, and when I get around to reconfiguring my sump, I'll add them back. They're kind of controversial as you've probably seen, if you researched them at all. My opinion, you can't go wrong in using them on a fish only system (most controversy is with whether they cause major problems with corals, I think). Especially with messy predators. I don't think they're a substitute for water changes or skimming, but I think they help uptake the nitrates/phosphates (naturally) so they are not used by other nuisance growth (cyano, algae etc).
For biopellets, I just suggest you build up slowly over time, as the products usually recommend,since going too fast can cause a bacterial bloom and those do get nasty. It doesn't hurt to have less biopellets than you need, but more than you need is always asking for big trouble. I took mine offline because I did get a bacterial bloom in my tank (cloudy water), which I attribute to my DIY setup not tumbling all the pellets consistently. I'll probably buy a reactor when I get them back online.
At the moment, my favorite nitrate reduction technique is my sulfur reactor. I was out of country for almost one month, with my parents to come by my house and do tank feedings, filter changes, ATO/skimmer stuff. I left at 5ppm Nitrates, came back to 80. My bluehead wrasse didn't survive, so my best guess is the harlequin tusk gave it a death blow and it died under a rock or something. So anyway, my point is, the sulfur reactor still had effluent coming out at 0ppm Nitrate.
