i was given a purple sea urchin by a friend and he told me they are good algae eaters. ( i think my tank is going through a mini cycle due to a tank upgrade. 55-90gal so i have a small diatom bloom right now) i am wondering if thats all they eat or if i am in danger of loosing any hard or soft corals to this thing?:madmad: he looks cool and i like how they get around. i have had it for three days and the best i can tell it is eating algae right to the rock itself! its like he is eating the top layer of rock. reason i say that is it is pretty clean (white) once he moves on.:huh: any help or knowledge on urchins would be helpful. thanks....

They are good nuisance filamentous algae eaters along with all macro and coralline (which is as you said, an accidental ingestion from their rasping teeth biting the algae down so far). They will not touch diatoms. Do you have more than diatoms in there? It won't touch your corals.

I have heard they are also sensitive to swings in KH. I haven't put this to the test with mine, but i try to make sure my KH stays around the same number.

They are good nuisance filamentous algae eaters along with all macro and coralline (which is as you said, an accidental ingestion from their rasping teeth biting the algae down so far). They will not touch diatoms. Do you have more than diatoms in there? It won't touch your corals yes, i have a minor hair algae problem i have it contained but just have not been able to fully get rid of it. (thats why I'm trying the urchin?) i also have a green algae that grows like the brown diatom algae. it grows on the glass and a few rocks. i need to replenish my clean up crew as i had a good amount of them die off due to a tank change. ( i think my tank is going through a mini cycle) i know i have a elevated phosphate problem. i have no choice but to use city water for my water changes at the moment. ( I'm working on a solution to fix that problem now) i noticed today the sea urchin actually ate part of the old skeleton from a brain coral that has been dead. i moved it off of that and put it on a rock with algae. he seems to only eat the algae on his way to the rock! i wonder if they need the rock in there diet or if they are getting calcium from it? it sits in a spot and i notice its waste coming out the top like little pebbles. will this damage my rock? i would rather it eat more of the green algae and the hair algae than what Coraline i have growing on the rock. id rather get rid of it and try something else! :) i have pictures but don't know how to post them in with my message? i don't know what my URL is? i am not use to pc's....:tounge:

If you are using firefox you can right-click on the image and select "copy image location." It will copy the image to the clipboard and you can paste the URL into the post.

Internet explorer sucks. I am not sure about how to use that one. There might be an option to "view image" in which case you can just copy the URL from the bar at the top of your window.

In Internet Explorer right click the picture and choose properties. You can find the URL there. That's assuming it's online somewhere, not on your computer.

I use www.photobucket.com to host my pictures. It is easy to upload them from your computer by clicking browse and just choosing the picture you want. Once they are there you can just copy the img code and paste it into your post.

thanks carmie, i just done that last night it got late but will finish soon. in the mean time here are a couple of the pics. of the urchin and some damage its done.

http://i221.photobucket.com/albums/dd241/clownfish4me/aquarium%20photos/215e1d34.jpg,

http://i221.photobucket.com/albums/dd241/clownfish4me/aquarium%20photos/822b0bf6.jpg

http://i221.photobucket.com/albums/dd241/clownfish4me/aquarium%20photos/8c7d42c4.jpg

http://i221.photobucket.com/albums/dd241/clownfish4me/aquarium%20photos/af965c17.jpg

well these are the only pictures i got so far, don't know why there a little blurry to me? hes ate more but will get the pictures later....

I had a pencil urchin in my BC8 for about a week. I got him as a freebee and thought I would give him a try. I ended up giving him to my LFS because he was "rearranging" my rock work, as well as munching on my frog spawn's skeleton. The unexpected bonus was the explosion of coralline in my tank. The white tooth trails were gone in less than a month.