pearling is one of the things i look for.
but not every plant will pearl significantly.
the best thing is the growth, but that takes time to see a difference, and its not always easy to notice. if you have any red plants, they get less red if CO2 gets worse (all other things being equal).
since your CO2 is high (if your fish are gasping), then perhaps its a distribution problem. any low-flow spots in the tank?
1+ It takes time, patience, and careful observation. IME, it is always come down to co2 and flow for co2 and nutrients distribution.