Can you post your tank specs? We need a more complete 'picture' of the tank to be able to really help. If you like, you can go into the Member's Aquarium Specs forum and create a post with all the details about your tank, then go into your user CP and edit your signature to contain a link to that page (there's a sticky at the top of the Members' specs forum on how to do this) - I've done this, it makes things so much easier than posting all your details over and over!
The most important things we need to know are:
Lighting (how much, what kind)
CO2 (are you injecting CO2? If not, are you using a carbon source like Excel?)
Test kit results (pH, KH, PO4, NO3)
Fertilization (what kind, how often)
All plants have fairly similar needs when it comes to nutrients, but some species need quite a bit of light as opposed to others. Some tap water contains enough of many required nutrients, but there are some you'll still need to add no matter what. Knowing what you're adding to the tank can help others pinpoint the problem if it's a deficiency.
