I change my KTP every time I do a WC but them again, I'm in Jakarta so KTP is easily available. I keep 3 in the tank and a small net back full in the sump.
I also dose with Tetra Black Water twice a month.
I have a SR and IT that are particular to black water, my tank sides are tinted to keep a level of darkness, I chose tint so that it wasn't pitch black.
I run a Current USA Freshwater Satellite Pro Plus so I can control the lighting to fit the dark ambience.
A pretty big community of fish.
Good Luck Bro!
https://youtu.be/OT7MfaAf3A0