As for the substrate you speak of, I have no idea.
I use flourite in mine, I've seen others with Onyx or eco complete.
As for the Phos-X......No, its not really good in a planted tank.
Well that depends really.
If your wanting to get into growing lush beautiful plants then you'll need to add trace elements, C02, ferts, and Nitrates to name a few.
Phos-X will remove phosphates yes, but it will also remove Nitrates.
So, it comes down to how far you want to go when it comes to growing your plants.
To be honest you can grow a variety of plants without all of the above and using the phos-x, but they'll be smaller, low light types that are easy to grow.
Heres a link I'm sure will guide you in the right direction you want to go:
http
/www.aquahobby.com/e_articles.php
scroll down the page and read the articles, I found them imformative myself.
