Black urchins :/

I recently added to my 15 gallon a black urchin and 2 crabs but the thing is i was reading some horror storys about urchin and how they eat coraline algae on my live rock so im scared :s cz im new to this thing ? so it will kill my live rock :/ ? i really want some colors :/

 

Not all urchins eat coralline, they do however eat one type of algae or another. An urchin can not kill your live rock by virtue of the fact that what defines live rock is the presence of beneficial bacteria.

Personally I would not put an urchin in a 15 gallon tank unless you can meets the urchins nutritional needs by supplementing the diet with nori or algae waffers.

 

+1 tank is too small IMO

What kind of urchin exactly?
Pencil urchin, Longspine, tuxedo?

Them eating coralline actually helps its spread in the long run because they excrete spores and specks of coralline which will settle in your tank and grow more. This won't kill your live rock because live rock is called LIVE rock because it contains bacteria that live within the rock. (lol that sentence sounds so weird)

 

Not a black urchin, but my tux has been in my biocube 14 for almost 2 years now and is great - I do glue everything down though. I have never supplemented his diet, but he may get some seaweed from rods food I suppose. He is about 1.5" from 1" when I got him.

 

If you have a coralline-feeder, and many urchins are simply because they typically eat more than they're fed/can find, it leaves white trails on your LR where they've gnawed the coralline away. Doesn't harm the rock, as mentioned tho.

I agree...assuming by "black urchin", you're referring to a Diadema sp. (AKA longspine urchin), it will quickly become too large for a small setup (think of a 12" ball of spines).

HTH