brown kelp in tank

[Zoaelite]

Well, first off all kelp is algae but not all algae is kelp. A photo would really help out, from the description in sounds like some sort species of halidima a macro algae. Species like tangs and Seahares are great for controling it but your best bet is to fix the problem, increasing flow, decreasing nitrate/ phosphates and keeping a steady system. What are your tank parameters right now?
Levi