The only thing that would bother me is the fact that I wouldn't know if one or the other method is working. Sure, both zeolites and pellets could be working, but because you run both there is truly no way of telling. It could be the zeolites stripping nutrients or it could be the pellets. In the end you don't know for sure, you just have to assume.
If all other parameters are fine and you truly are running an ULNS then then I would say you should look beyond just the removal of nutrients for your unsatisfactory SPS colours. As you have already done, lighting is one factor. The inclusion of certain nutrients is another factor in a very long list of others. Heck maybe how your SPS looks now is their natural state
