Little Crabs?

It could be fry, but most likely they are pods. Amphipods or copopods. Do a search, Mark P. posted pics not too long ago.

Are they bad or good?

That's right, the 1/4" to 3/8" white half moon shaped things are Grammerus, a type of Amphipod. kind of like a shrimp. They are good algae and detritus eaters. They live in the sand and the rock.

Copepods are much smaller animals that look like white dots. They mostly stick to the glass and rock surfaces.

The little swimmy things, when first noticed, are often thought of as baby fish. They are actually a shrimp of the Mysid family, Not mysis shrimp like the frozen kind we feed to the tank, but MYSID Shrimp.

The fact that you see Mysid shrimp tells me something about your tank, especially that it's in really good shape, otherwise you wouldn't have those little critters swimming around. The algae that you hate so much has kept the tank relatively clean. I cannot say why you have lost a few fish lately, except that death happens and like I told you on the phone, too much algae growth can sometimes be a problem. Perhaps the Tang will help you control the algae but hopefully won't eat all of it before you get a refugium going.

Grammarus, Amphipod


Copepods and a stinging Hydroid (greatly enlarged)


Sorry, I don't have a pic of a Mysid shrimp just yet.

Try looking in your tank at night thats when all mine come out scared the crap out of my too luckly until i figured out what thay were there was no reason to reach in my tank