Hi every one i got this weird relish purplish alage growing fast in my tank I got a 75 with 2 hqi and 4 to bulbs nitrate is almost always zero and I do weekly 5 gallon water changes with red sea pro I'm worried because the alage is growing over my coralline and I don't know if it will harm my coral it's very course does not grow tall grows more like a thick woven mat and is hard to pull off the rocks my yellow tang seems to nip it but he could also be grabbing organic stuff that get s trapped in it so I'm unsure if any one knows any thing about it plz help Thank you every one