I've been using av fuel due to having zero phosphates and nitrates. I think my sps were starving so I've been using it for month or so. My frags are encrusting really fast but I'm not sure whether it's because of that or not. I use a small amount but it's definitely nit hurting them. I stopped using gfo and started feeding more. Once I get my phosphate up a tiny bit ad well as a small amount of nitrates I'll probably stop using it though