Lose the sand and switch to all paper towels. Could be from scratched from the sand or maybe even the other gecko. Looks like it may be infected though. I would flush it out with warm water at least. Get it to a vet asap!
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Leopard Geckos:
1.0 Normal
1.0 Red Stripe 66% poss. het. Tremper Albino (West Coast Captive Breeders)
0.2 Tangerine Carrot-tails

1.0 Bearded Dragon (Sandfire Yellow/Orange)
1.0 Three-Toed Box Turtle (Rescue)
0.1 Albino Ball Python (BHB Enterprises)

Bird:
0.1 Jenday Conure

Pups:
1.0 Black Lab/Pit Bull
1.0 Maltipoo

Fish:
Jamaican imported Wht/Blk/Gld Angelfish
Roseline Shark

-Patrick