My use of pumice and kitty litter is heavily influenced by a group that calls itself the Swedish Plantguys. Their recommendations are grounded and usually accompanied by a (sometimes extensive) science lesson. I try to link their piece from YouTube on pumice but because I'm a new member to this forum, I can't.
For my personal use, it was between this pumice mix and Al's gritty mix (pine bark fines, Turface, gran-I-grit). The basis for these mixes are similar (ability to provide good drainage and aeration while retaining moisture) and I just find it easier to source pumice as opposed to Al's ingredients. When added to pumice, vermiculite or clay (sourced here as kitty litter because it's cheap and readily available) serves to bind fertilizer and release it to the root.
As for the plant, I didn't remove or replace any of the original soil. I just up-pot the entire thing and then fill in the rest with pumice and kitty litter.
The plant is next to the front door that faces southeast, more towards south than east. Above the door is also a large 4'x6' window, maybe even bigger. Although it is not in front of the window, the plant still gets plenty of indirect light.
I'll start watering from the reservoir now and see if it improves.