Well thanks both of you, I guess I am doing ok then. Will know better when I weigh them.
I am also having trouble trying to get them off muesli type dry food. When I got them at 8 weeks, they were on a muesli type food, so I bought the same but have found that they don't like yellow bits or little wheat seed bits, they are always left at bottom. I bought some nuggets from Wilkinsons and mixed in with their usual butt they were not impressed, so now I am trying this-
http://www.petsathome.com/shop/woodlands-guinea-pig-food-and-forage-750gm-and-2kg-15713
I thought they might go down better as it has hay in it as well as nuggets, but so far they are fishing out the old stuff.
Should I just let them have muesli and ignore the bits they won't eat or keep trying with nuggets, I don't want to upset them by changing all time.