Guinea Pig urine colour

Question
Sounds odd, but my guinuea pigs urine is a bit whiter than normal.  I have looked at information on the internet and it says to remove some calcuim from their diet ... Can you give me an idea of what I need to remove? Is it in the hay?  Baby Spinach?   Food pellets? or Ginko Plus?  Or just as an odd thought should I filter their water as we live in a hard water area?
Thank you for any help you can offer.

Answer
Hi Philippa

This is totally normal but I have included a link below which gives the foods in order of their calcium content so you can look and see which you feed and reduce accordingly.

Dont stop feeding hay, thats definately not the issue.

Andy

http://www.guinealynx.com/diet_vegs.html