Plant Substrate'

[jeff_hopkinson]

hi, Is there a plant substrate that you can use with sand and how would you use it. I have two 40gal tanks whith sand substrate and both are planted but with only sand the roots on some of the plants are turning black. I am sure i have read a letter on site were some one put plant substrate on top of his substrate and it looked quite good. I have also been advised to use a substrate of silver quartz. ANY help will be appreciated.