Thanks for the feedback! I have kept quite a few successful NPTs in the past but only experimented w/ Excel in two of them. Filterless never seemed to be a problem but perhaps I may have seen better growth w/ circulation. Diana brings up a good point; using a pipette or turkey baster to "feed" plants lower in the water column might be something good to try.
Roy, thanks for helping me realize the possibility that CO2 may not have been the limiting factor in that tank. This was a 20 long w/ an Ecoxotic E-series fixture and back then I was also experimenting w/ PPS Pro. Your comment made me realize that I was probably making things worse by continuing to add ferts to a tank whose plants were not thriving (they just sort of existed lol). I have seen quite a few tanks that grew more difficult plants w/ medium light as long as CO2 was supplemented, which is why I wanted to try Excel in that tank.
I wonder if the E-series fixture was still too weak. The lighting was definitely less intense than the true NPT I had before that which was growing R. macrandra surprisingly well.