Boiler Anti-Corrosion

matty_c608

I meant would it be necessary to top up the inhibitor now, not drain the system (bearing in mind just half a bucket of water came out).

I think a 'test' would be necessary of the water to see if nails rust. If they do, then I may have to top up:::

If the nail becomes rusty, how would I calculate the amount of inhibitor required?
How long would I leave the nails in?
Is a 'tester kit' better than doing the rusty nail trick?
How does the tester kit work? Is it a special nail?
What material should the nail be that i test with (Not Aluminium for example)?