I think your chasing an invisible enemy here (regarding SPS)"¦You might have been feeding a little much, and the food grade cans may be an issue, but how long has your tank been fully up and running? Based off this thread, I'm seeing something like 3 months maybe? Regardless of where your numbers are at (NO3, ALK, Ca, etc.) there is something special about a mature (aged) tank that you just can't measure"¦I think that might be your main problem (with SPS specifically). Give your tank a good 6 to 8 months and add things slowly to ensure the tank is ready to support it.
Another good indicator is coralline algae. I see people throwing SPS frags in tanks with no coralline algae on the rocks and wonder why their SPS die. If your tank can't support coralline algae, it most likely isn't ready for SPS corals"¦Likewise, if you have great coralline algae growth, you'll likely have great SPS growth. As with anything, this varies from tank to tank and coral to coral, but I think coralline is a good (basic) indicator for SPS (and overall tank health in general)"¦
Just my thoughts"¦Best of luck"¦I still have some easy SPS for you when your ready"¦