More testing the next day late afternoon (previous samples were also late afternoon).

Soluble Iron zero

Total Iron also looks like zero

BYPASS softener

Soluble Iron zero

Total Iron about .1ppm.

BYPASS softener, centaur carbon, and second Katalox Light tank

Soluble Iron 7-9ppm

Total Iron not tested

BYPASS softener, centaur carbon, and both Katalox Light tanks

Soluble Iron 9-10ppm

Total Iron not tested

Notes:

Total system is under ideal conditions resulting in no measurable iron
Softener isn't removing much iron

Second Katalox Light tank with Centaur Carbon tank are removing a great deal of iron.

Even with chlorine injection/retention time, calcite tank, and one Katalox Light tank 7-9ppm of iron remain in water.

I would have expected half that number or even less. Is the first Katalox Light tank doing its job?

The second Katalox Light tank and Centaur Carbon tank then remove almost all of that amount with softener doing a small amount of polishing.

As ditto suggested I should: "Backwash the KL tank and see how much iron is coming out during the backwash cycle. Once the water runs clear you should add several minutes after that in the backwash cycle. Be sure to have an adequate rapid rinse cycle."

I should also test the backwash of the softener. If the softener backwash contains iron then the toilet reservoir tank problem could be due to insufficient backwash time and/or use during regeneration?

Below you first see the total iron test of water out of the softener.

Second is the total iron test of water bypassing the softener.

Third is soluble iron test of water bypassing KL2 and Carbon tanks (this result was virtually indistinguishable from the test after bypassing both KL tanks).\