Newbie - Local Experts Dumbfounded

[Wh1t3Rabbit]

Hi, I have a tiny new tank, 2 clowns, a hermit crab (from Hilton Head beach 2yrs ago), a Pistol shrimp and his pal the goby, an Emerald Crab, and 4 snails.

Earlier today with the tank light on, I was watching the tank when something that looked like a shiny, flat, pumpkin seed “jumped” off the faux coral (see the purple rock in the picture attached) and darted along the bottom and under the rock (where the shrimp and goby hole up). I’ve not added anything lately except 2 pieces of what we thought was pretty heavily bleached rock from the ocean from last summer. It’s been sitting out in the sun and dry for at least 4 months now. The only other things we’ve added lately is 2 more snails (who have completely eaten all the algae so my Emerald appears to be scavenging now, dangit, but that’s for a different day.

I’ve done some searches, and I have NO clue what this is or if it’s good/bad. I can’t seem to take a picture of it because it’s SO fast and hides under the rock and blends into the crevices and dark corners. Anyone? Do I need to be concerned? Nothing appears to be hurting except that my green algae is definitely gone eaten and my tank looks like I just bought it yesterday.

 

[Mr Fishface]

Alright so here is my best guess. Sand skaters. Small, look orange, and move fast. Does this look familiar to you at all?

Sand Skaters | Melev's Reef

One day I came across these very tiny pods. These are so small they are rarely noticed, but I was dipping some new zoanthids to make sure there were no pests and these little guys came out into the open. After checking with Dr Ron on the Marine Depot forum, he and others identified them as...

www.melevsreef.com

 

[Wh1t3Rabbit]

Alright so here is my best guess. Sand skaters. Small, look orange, and move fast. Does this look familiar to you at all?

Sand Skaters | Melev's Reef

One day I came across these very tiny pods. These are so small they are rarely noticed, but I was dipping some new zoanthids to make sure there were no pests and these little guys came out into the open. After checking with Dr Ron on the Marine Depot forum, he and others identified them as...

www.melevsreef.com

Nope. This literally looked like a black sunflower seed. From the second or two I saw it out of the corner of my eye, it darted and moved quickly across the bottom of the sand, and then in a blink was gone under the rock.
I wish I could figure out what it was, and whether it is OK or bad for the tank.