add substrate to existing or replace?

[pshawk]

i have a 75g that i want to turn into a planted tank. it already has about 2" of traditional gravel in it. so, should i replace the gravel or just mix in a good amount of flourite? the end goal is a tank of rams and discus with a dominate piece of driftwood and moderately planted.

 

[fish n chips]

it will be fine to leave it in i think as long as its not sharp

 

[pshawk]

2-3mm rounded gravel