my guinea pig has a bald spot!

[workshy]

my indoor piggie has a bald spot by his shoulder
the skin where the hair should be is darker than the skin on the rest of his body

the other pigs he lives with seem fine and they are all getting along with each other -no fighting or anything

is this mites? (can see any mites on him??)

Ringworm?

workshy have a look on Gorgeous Guineas- they've some some photos and 'differential diagnosis' that you can compare.

I've bought something from Amazon Xeno 450 which treats and prevents mites,lice, ticks and internal parasites (roundworm IIRC) but not ringworm.My boys haven't got any signs, but now they are out at grass when it's nice I'm worried about worms from passing animals on the lawn and ticks.

Early stage mites leave a dusty, scurfy sort of dander/skin.
Lice would be visuble.

Does your GP scratch?
Have the other pigs been nibbling his hair?
Is the skin crusty or scabby at all.?

It might be worth ordering some of the Gorgeous Guinea melts and some of their treatment shampoos.
They have a huge choice for different conditions. I bought a selection of their trial bottles.