Yes, Flourish Fertilizer tabs, by SeaChem. Each tab covers a 4-6" radius, and lasts up to 3 months, though realistically mine lasted 2 months before they were totally dissolved.
They're ok, but you can actually make your own root tabs very cheaply if you have access to the right chemicals. mostly you need a clay powder, and some plantex CSM as base ingredients. www.plantguild.com
sells all the supplies