yellow water from new HW tank - RESOLVED??

[Al Reuben]

I replaced one water heater in my home 10 days ago. It is a secondary unit I use in my basement for my fish hobby and services one sink, one faucet, only. Its a 40G unit.
My main water heater is a gas unit.
My water is well, has an iron treatment unit and then a water softener. The water to the secondary tank is treated for iron but does not get softened as does the water to the main gas heater.
My water throughout the house serviced by the gas heater is crystal clear, no problems.
10 days ago I changed the secondary unit. From the day of install it was putting out yellow water. About 3 days after install I called the MFR and they had me empty water from the pressure release valave - it looked like yellow curry, very dark for about 1/2 cup and then a lighter yellow. The supply line for the cold water to the HW tank is off the same cold water line that runs the cold water tap in the sink - perfectly clear. When the new tank was installed, new pex lines were run for supply and output to the sink, as well as a new faucet. After 10 days, the mfr agreed to replace it.
We replaced it 3 days ago and the new unit is putting out yellow water again. When they disconnected the supply water, it was clear.
PLEASE NOTE: The replacement unit I received had a 1 digit difference in the serial number - ended in 239 rather than 240, indicating to me that if there was a production issue, that would possibly affect several tanks.
I called the MFR a second time and they tell me it has to be the water, can't be the unit. I told them about water parameters everywhere else in the house. I asked them to send a plumber of their choice to check it out - if it was water supply that would be my issue. If not, there is a problem with the tank again. I suggested maybe a pallet dropped?? when there is a brake recall it is 50,000 units not 1 or two I suggested.
Any thoughts on my yellow water issue??

 

[Al Reuben]

I contacted Culligan today and they felt that if my iron treatment unit wasn't running at par, it could absolutely contribute to the yellowish water in the HW tank - heat, oxidation, etc. They also felt that as the main HW tank water supply was being treated twice - iron treatment AND the water softener, the water softened would also remove some of the iron. The iron unit is 12 years old and they are going to come out and tweak it or replace with a newer unit? While they feel I couldn't see any coloration in the cold water tap, indeed the iron was there in solution and when heated up came out yellow. I'm hoping they are correct.