Urchins and tank size

[ThunderGoose]

I have a 55 gallon ID tank with 2 urchins - a nice female tuxedo (she has "spawned") and a roughly 4 inch hitchhiker who came in on live rock from Tampa Bay Saltwater. The unknown hh urchin has been scouring the rock, exposing the white under the algae (I think it's her but I have a lot of different inverts). I'm thinking there's not enough food / too many competitors. I do feed Nori several times a week.

Should I rehome the bigger urchin? Could it be something else? I have a starfish, black elephant limpet, money cowrie, snails, mini hermits. She's fun to watch but I have no plans to get a bigger tank anytime soon.

Thanks

 

[hijinks7]

I had an urchin that would leave a trail of white wherever it went. Probably just how it eats. I'd just re-home the unknown one and keep the tuxedo. I think the min tank size for a tuxedo is 20g. The unknown one who knows.

 

[nautical_nathaniel]

That sounds like the work of an urchin to me, mine goes around and eats coralline algae and in the process will usually make the rock white where it has eaten. Urchins really don't need a whole lot to eat but it does look like it is getting fairly large and may cause some problems with knocking stuff over, stabbing corals with their spines, or picking up and moving small rocks around.

If you feel like its not getting enough to eat (i.e. all your rocks are white) you can stick nori in it's path or shove it in a crevice in the rock for the urchin to find later. If you think it's getting too big I would try rehoming it first or donating it to a local aquarium (if they determine it's a local species).