I'm pretty sure what you have are anchorworms. I'm having the same problem in my 240, currently treating it with cyropro from Hikari. Is there swelling where the worms attached themselves on? Anchor worms start out really small so you might be going through the early stages where they have not reproduced yet luckily. I ignored mine for too long and now theres a chain infection. I have about 3inches thick of sand and i have no idea what i should do 
