Thanks for the replies,
I've got most of my info on cloning from this page
A batch of clones in rockwool - Grasscity.com Forums
and the guy who wrote it said that the cubes should just be damp and not soaked.
Might have to try dipping them in water next time and using less lemon juice.
The PH was around 5, but all that was used was one of those cheap water testers (I'm not sure how accurate they are)