How and when to split moss balls?

[gm72]

Question is the title. Anyone who can help? I think you can split them at any stage but best when they are at least 2" in diameter. Use a sharp knife?

[Fishalicious]

When they are ready to split I can usually feel as they get a bit lose it and just do it with my hands.

[cocoa_pleco]

i just slice em with a scalpel