Besides from the good information you received already, if you have alot of Seiryu stone it will definitely raise your KH anyway, sometimes substantially. My KH goes from 4 (tap) to 8-12, depending on water changes. I've had endlers in tanks with kh 4 and now with the 8-12 and noticed no difference. One of my endlers is going to be 4 in November. I also have a ton of RCS and some amanos and there is no problem with large KH swings after water changes.
Very good to know endlers and RCS should be fine based on the water parms.
I was hoping the stones would raise my KH some. They sure fizzed a lot when I vinegar washed them (vinegar made them look spectacular). But so far after 4 days submerged, they have not changed my KH beyond my tap water but going to test everyday, maybe it is a gradual change.
The API KH test kit doesn't have very high resolution, I go to 4 drops, which is "50-100ppm" which is KH 3-5.
I like the API tests but maybe there a more precise test or method for KH, need to research that on these threads and maybe start a new thread.