Best thing to do is to take it very slowly, don't add the full amount at once. The stories of failure you've heard have been from people who (in general, for the most part) who simply didn't study up and follow the rules of pellet use. The amount used is based on water volume and is generally an educated guess of total volume. I'm sure you have some general idea of what that is. I would keep the GFO for at least three to four weeks after starting pellets, the pellets take a good six to eight weeks (probably depending on which ones used) for the pellets to become colonized and useful. You can't really add too many pellets, the bacteria that colonizes the pellets can only survive if there are enough nitrates and phosphates for them to consume. The biggest problem from pellet usage is when people just add the total amount used at one time and strip the water too quickly, and the second is alkalinity burn on SPS.