I've had this snake plant for quite some time, but recently one of the leaves has been fading in color.
The mix I'm using is perlite based, and I water it once a week. I give it sunlight in the mornings, and in the evenings I put it back on my table away from the window.
What am I doing wrong? Should I cut that leaf off? Also, I want to use rocks instead of perlite mix. Can I switch to rocks only? Will it grow with only rocks?
The yellow leaf is on the outside of the rosette, which means it is the oldest one, so yellowing and dying off is natural as new leaves grow out from the center. You can cut it off if you want, or wait for it to dry off, and cut it dry (there is slightly less risk of infection doing this).
Indoors, Morning sun is good, but your plant looks slightly etiolated. If you could give it as much sun as possible through the day, that would be great.
Your perlite-based mix is good, as long as you are fertilizing occasionally. That type of mix washes out easily, but at the same time Sansevieria are sensitive to over-fertilization. Fertilize lightly, and occasionally. Your watering schedule sounds good, letting the top of the mix dry out in between waterings.
Snake plants like being pot-bound, so even as it grows, try to keep it in the same pot. As for moving it to stones, this plant isn't an epiphyte, and it isn't well adapted to aquaponics, so any method of growing it on pebbles won't be best. You can, however, place a layer of pebbles onto the top of the mix, for the same look, but keeping the plant in its original mix.
