Black/Grey dirt out of new faucets

[PatSea]

I just recently had a complete remodel done on my master bath. It includes a new 2.5 gallon Tiny Tot replacement electric water heater in one of the cabinets to provide instant hot water to the two faucets since the main water heater is a long distance from this bathroom. As soon as we started using the bath we noticed black/gray particles coming out of the faucets into the new sinks. It looks like someone took a pepper shaker and sprinkled black pepper into the sinks. I've run at least 200 gallon of water to try to clear the debris but it isn't clearing up. There is as much debris now as when we first noticed it. The particles are not oily and not hard. When I grind them between my fingers they smear into a dark grey film. What could be causing this debris?
One other piece of information. The contractor connected the main hot water supply from my 50 gallon main water heater (soft water) to the outlet of the 2.5 gallon water heater. The inlet side of the heater was connected to the faucets. He got the inlet and outlet reversed. Is this part of the problem? I hope you can make sense out of all this.
Any ideas as to what is causing the black partivles?

 

[Dj2]

Any other faucet around the house having this problem?

1. Reverse the IN and OUT at the instant water heater. Problem persists?

2. Bypass the instant water heater. Problem gone?
If yes, then it's the small heater. If no, it's something else.

 

[Sponsor]

 

[Master Plumber Mark]

We have come across this same problem before....
Our problem took a while to show up but it had to do with using
Brass Craft black flex connectors on the water heaters... They look like black hoses
and work real well to hook up a water heater fast..

The problem was aggressive water
that attacked the poly rubber liner inside... we were getting black flecks
that smeared when you touched them.... Only had a few issues with them
but had to change to SS connectors

I dont know how your contractor hooked up your heaters but
if they were used that is most likely the problem