Pond liner to separate Substrates?

[greaseball]

I'm going to turn my 55 gallon tank into a planted Discus tank, and I have some gravel I would like to use, but I would like to have laterite or some other plant substrate beneath the gravel. I dont want the two to get mixed so I came up with the idea to put some type of pond liner between the two substrates and when i want to place a plant into the laterite I would just cut a slit in the liner. What do you guys think? Any other suggestions?
Also how many watts of light would I need for CO2 to be effective?

[TwoTankAmin]

There is no need for using the liner. The laterite stays in the bottom layer where it belongs, so will a fluorite base. On the other hand, the liner will prevent the stuff you want to filter down into the substrate, which is beneficial for the plants, from doing so.

Co2 benefits plants at almost any light level but is not needed for lower light levels. However, once you cross above about 2 wpg and head towards 3 wpg, co2 is needed to keep everything in balance and the algae at bay.

[greaseball]

Thanks, thats what I thought, but I was a little concerned about them mixing over time and making an ugly mess in my tank.

[Jeremy S]

Why don’t you just use flourite (http://www.drsfostersmith.com/product/prod_Display.cfm?siteid=6&pCatId=4870) instead of laterite?