SPS not liking GFO is a load of bologna. SPS don't like fluctuations in water parametes. MANY reefers use GFO with SPS dominate tanks with no problems. The real issue is that GFO requires a somewhat steep learning curve. With anything though, you do your research and GFO becomes something that isn't that difficult to implement. When you start with GFO you need to really take it easy on how much you use until you see how your phosphate drops. Once you have an idea of how fast and much your phosphates dropping you can start to adjust how much GFO you're using. If your only goal is to use GFO to reduce PO4 below 0.1ppm then, GFO becomes even easier to use. Its when you ride that line between 0.03ppm and 0.00ppm that creates issues quickly if you get it wrong.
Pellets arn't bad, but really you just need to feed 3-5 pellets per fish. If you count that up, you'll realize it likely wasn't the food causing PO4 issues, but a heavy feeding hand that was.
Also, make sure your tang is getting nori a couple times a week. Tangs need a prominently algae based diet to maintain a healthy body. An interesting point to this is that this could also potentially help your nutrients. Tangs bodies are not meant to process proteins from shrimp. Can they eat them? Yeah absolutely. Will it kill them? Probably not. But when an animal cannot properly process the food its eating, its excreting lots of beneficial nutrients to the fish. IE: Nitrates and Phosphates. So theoretically, feeding a diet that the fish can more efficiently digest and utilize will also lower nitrates and phosphates because they are being used for growth instead of just being passed through the animal. Probably something that is inconsequential on a test kit, but for the animal can make a big difference.
