Why does this happen??????

well its a powerhead people put them in their tanks to provide flow for the livestock.

 

It's purple coraline algae, perfectly normal and harmless. Many people actually want it in their tanks, myself included. Eventually it will cover all of your live rock. If you don't want it, start scraping, but good luck. In my opinion, it really does make a tank look more interesting. Also, your calcium level is very good and probably your other mineral levels are also good for it to be growing. Enjoy it.

 

coralline

 

'cause coraline will grown on anything and everything thats in the light.

 

Especially plastic and glass lol. You want it until your arms ache from scraping then you curse it.

 

See, the thing is, I know when I first saw coralline I imagined it only on the back wall - not quite all over the front glass lol.

 

well I didn't imagine it over every single in the tank that wasn't flesh. I actually hate purple now.

 

^ , that was a good one!
But yes,coraline will attack plastics (theres a thread somewhere on where someone put a plastic model airplane in his reef to see how quick it got covered)and it's a sign of good water,plus wherever it encrust,typically other bad algeas can't grow.

BTW-Welcome to 3reef!! And nice looking tank!

 

glad someone thought it was funny lol