Flourite is messy at first, need to rinse it *really* well. I just did three bags of it in my new 55 and I did 4 water changes after I'd already rinsed it. I did a small batch at a time in my homemade strainer, put it in the tank, filled it up and started on the WC ritual. Was my first experience w/ flourite. I dropped some good ol Missouri River rock on top of it and it looks pretty good now.
I think your going to have to redo the tank. Drain it, put all your fish in another tank, pull everything out. Put in 2 inches (if you can afford 2) of flourite in the bottom after you rinse it, then put your pea gravel on top (about another inch). Fill it up, do WCs if the water is cloudy, plant and readd your fish once your satisfied with the water parameters. I don't have any experience myself with mixing but I imagine it would work just fine unless your going to clean your substrate with a gravel cleaner like you would on a normal fish tank. Flourite doesn't clean too well in my (limited) experience. I use a python cleaner hooked up to the faucet or outside hose, and it'll suck right into the tube and get flushed if your not careful. Cleaning a planted tank is a bit different than a normal fish tank tho.
If your not going to plant it very heavily, might consider 'potting' your plants in some containters (bowls, small glass containters, etc) and putting flourite in them, will save you a bit of coin.
If you've never done plants before, and your serious about keeping them, you can go about it a couple of diff ways. Redo the substrate and stick in some plants and possibly struggle with it, or do some solid research beforehand on what it takes to keep a planted tank and then dig in. Read them stickies, over and over, is what I did until I 'got' it. That is, after I did my first option of sticking some plants in my tank and wonder why they didn't do well! Wyld's posts are solid - they have alot of useful info. Lighting is makes a huge difference and there are alot of different kinds and most of them do you about zero good with plants in yer tank. Water quality IMO has alot to do with it as well as the fish your keeping. I still don't know if all the trouble I had was because of pi$$ poor water quality of it my plecos and such were eatin my plants.
Anyways, good luck on planting it out! Can be alot of fun figuring it all out IMO, I'm still in the process myself!
