Guinea pig dandruff?

[menagerie]

Was grooming the guinea pigs and noticed they both seem to have dandruff quite badly. They had it when we first got them but that seemed to be caused by mites (which they had, untreated, in the pet shop.) But there's no sign of mites now. They seem well. They're lively, chatty and affectionate, but they are lying down a fair bit which I don't remember them doing so much before. They are 18 month old neutered brothers.
If anyone has any idea what it might be, I'd be grateful for tips. Don't really want to shampoo them unless I have to as I tried once before and I thought they'd die of fright so gave up pretty quickly.

sounds like mites tbh sometimes they don't seem to get ill with it, sometimes they have scratches under their fur but they are hard to see
just buy some ivermectin online and put it on behind the ears/on the bum. depending on how much they weigh you can either buy the ivermectin for small birds (think it's 0.1%) or the 1% for large birds/rabbits/guinea pigs. the instructions are all downloadable so you can check the amount you need
www.pharmaqwebshop.co.uk/products_detail.asp?SubCatID=13&productID=65
be careful with it and the dosage - weigh the pigs first
it's usually repeated every week for 3 weeks I think but check the instructions for more detail

Thanks merci bucket, for the advice and the link. They have been scratching a bit but not too much. I can't see any live mites but better to be on the safe side.