John wrote:
Can you put too much of this stuff in? I presume not really. The reason
for the question is I have just drained and refilled my system and added
sludge remover. When it has done it's job (2 more weeks) I need to drain
down and refill adding inhibitor. The bottle says for up to 10 radiators,I
have 12, can I just put 2 bottles in or will it be OK with just the one. If
it helps it is not a sealed system.

It's volume which is important, not number of radiators.
Me, I'd put 1.5 bottles in, and keep the .5 for when I need to get the next
bottle for refill.