tankless flush turned bad...help!

[storvil]

Flushed ecosmart27 to descale it. After 30 min the vinegar was blue (normal, I should've stopped here). After 90 min the solution was clearer but the bucket was covered in grimy, grey, greasy coating (see pic). Dry, it's grey soot that smells metallic.

Any ideas to clean this stuff out of heater now? How would you service it?

Any idea what went wrong to cause this?

 

[TomFOhio]

Try running clean water through it backwards.

 

[storvil]

you're such a good person.

 

[TomFOhio]

I'm serious. I flushed them backwards with clean water after flushing them with the biodegradeable solution.