Thanks guys, corrosion was my niggling worry Geof. Mazak, thanks for the advice. I'll change coolant, wondered why mine was so cheap and now I know the answer

My problem is I don't use the mill for like two weeks, most of the stuff I do is diamond machining on a different beast, so my mill can be sat there for like two weeks with the coolant suppurating. I can't justify running an aerator 8 hours a day electricity wise (electric bills have just hiked about 30% here in the UK).

I'm sat here 30 feet away from the mill in a different room and I can still smell the bloody stuff. It's one of them horrible damp smells that really annoys you. Can't concentrate on the maths I need to do because of it.

I won't add bleach. I was worried about corossion and if you, Geof, are worried too then that's good enough for me. I'll change the coolant as per Mazak's suggestion.

Thanks again chaps!