sps dying/bleaching -- bad carbon?

Soooo I've had pretty good success keeping corals but as of late, a lot of my sps have been bleaching. Its a few select colonies and pretty much only on one side of my tank. I think the problem may be the carbon I switched to recently. Has anybody had any adverse reactions the marineland carbon? My lights have been a bit off too but I don't think its been enough for a whole colony that's been in different lighting several times to just up and bleach like this. I also suspect it since that's the side of the tank that had the carbon flowing nearest. Its also been happening since I switched the carbon. All my levels are in good levels:
0 nitrate/nitrite/phosphate
500ppm cal
9dkh
1400 mag

water change just a few weeks ago but after I noticed the coral struggling. Flow is sufficient. I decreased lighting just to be sure and that had no affect. Carbon has been the only other change. I removed it today.

How much carbon are you running and for how long? Are you running GFO? What are your parameters?

If you stripped the water of nutrients too quickly or made the water too clear too quickly, then corals will bleach. If you're thinking it's a problem with the carbon itself, then it's possible, but unlikely (happened with Kent though). Kent had a copper contamination problem, which is usually seen with inverts dying, reds draining from SPS, and eventually coral death. I haven't heard of any problems with Marineland though.

Edited by ReefdUp - October 14 2013 at 8:30pm

As I have been struggling with sps might not mean much but most sps prefer .02 PO4