When I do a test with the color block apparatus, I am getting an FC reading of about 2.5.
When I then do the FAS/DPD test from the TFT-100, I am getting an FC reading of 8.

I believe the color block test more than I do the FAS/DPD right now, which is not the way it's supposed to work!

I lost the small blue scoop used to put the powder in the test cylinder, so I have been estimating with a different small scoop.
The amount of powder always struck me as pretty subjective anyway, but I'm wondering if this is where my problem is.
When I put it in the cylinder to test FC, the water is a brighter shade of pink than I ever remember it. Is that a result of too much powder?

I have had my kit for just over a year. Can the powder go bad?

Thanks!

Use the OTO test (color block/comparator) to test for the PRESENCE of chlorine but do not depend on it to test the amount accurately. Have faith in you FAS/DPD.

The amount of powder used is not critical. You simply use enough that the solution turn pink/red.

The brighter shade of pink would suggest a higher FC.

If the DPD powder turns the solution pink, it is not "bad" and the test is valid.

I agree with Dave about trusting the FAS-DPD but to convince yourself, take a sample and dilute it with half chlorine free water and test it with both kits. See what you get that way.