Last night I made my first batch of EIS on an automatic Silver Puppy using the SWAP setting.
Distilled water tested 000 in to a 16 oz jar.
The silver rods darkened so I wiped them and nothing came off.
After ~3.5 hrs the lights were off and it tested 005 on my little Hanna TDS meter.
Liquid is clear.
In anticipation of the next batch I wiped the silver a little harder and got some tarnish off, leaving it shinier

Is it ok to use a metal canning jar lid?  If not, why?

It is my understanding that without a more sophisticated (expensive) tester there's a factor I can multiply the 5 by to approximate ppm of silver. It is also my understanding that it doesn't matter much.

Is this correct?

Thanks.  Saralou