finally replced the 50/50 sand and gravel in my 40 gal planted to 75/25 special kitty/sand. Did the whole thing in under 4 hours without tearing the tank down and taking out the fish. Took me about an hour of rinsing to clean the litter. Laid down about 3" of 75:25 littler:sand and then topped that with an inch of pure sand. Tank looks awesome and all the fish seem to be fine.
Just wanted to let ya all know of the experience.
I also soaked the litter with liquid iron for a bit before adding to tank.