I've had my 20 gallon for a while now and I've got a purple urchin 2 black clowns a neon gobie and a purple fire fish.also a few turbo snails and blue leg crabs. I've lost 2 pepermint shrimp for mysterious reasons and this morning my firefish was dead and I can't find my gobie. My water was tested not too long ago and it wasn't really anything wrong with it. I don't know what could be killing things and tje only reason I can come up with would be my urchin but I dnt even know if they sting and kill fish like this I'm at a loss. And I'm worried for my coral. Can any one help I'm all ears