3 Q's: urchin, starfish, nitrate

[americnjewl]

1. We have two short spined urchins and it seemed like one got smaller (pink) and the other got fatter (purple). They've been eating and moving around the tank with shocking speed. Do they grow and shrink around their spines? Is the purple guy losing spines? I don't see any in the tank.

Here's what the purple one looked like when we got him:

2. Just added a sand sifting star this weekend. He's mostly been in the sand and we were advised by the LFS that if he's on top of the sand, he's probably looking for food. I gave him some red seaweed and when I checked back it was gone. What do you think? Is he okay?


3. My nitrates are probably around 15ppm. How concerned should I be? My ammonia and nitrites have consistently been at 0 (weekly checks).

75G tank

 

[blaxsun]

1. The just tend to grow fatter in my experience. The occasional spine loss is normal.
2. Yes, more than likely he's fine. Sand sifting starfish will spend most of the time under the sand.
3. Myself I wouldn't be concerned (my nitrates are above 35+ and my urchins are fine), but a good target to aim for is around the 10ppm range.