I just skimmed through this thread and apologize if this had already been mentioned. Since pearling could also be an indication of O2 saturation, perhaps the non-pearling aquarium is low on oxygen? I had a similar experience where all of my other parameters were in line, but the plants did not pearl much. It was like this for several weeks before I suspected an O2 issue. My remedy was to raise one of my Lily Pipes slightly above the surface to agitate (and in turn, oxygenate) the water. One could predict that this would lower the CO2 levels in the water as well. I did not alter my CO2 bubble rate intentionally for this "experiment." With the pipe raised I got pearling in a day or two that was out of control.
I was able to repeat the "experiment" by lowering the outflow to its original position. Pearling decreased dramatically. So now I keep one of the outflows just slightly above the water surface all the time. Plants pearl nicely.
I was able to repeat the "experiment" by lowering the outflow to its original position. Pearling decreased dramatically. So now I keep one of the outflows just slightly above the water surface all the time. Plants pearl nicely.