What can cause a well water sample to turn pink, using the modified colitag media?

Document ID

Document ID TE1145

Version

Version 4.0

Status

Status Published

Published Date

Published Date 04/12/2018
Question
What can cause a well water sample to turn pink, using the modified colitag media?
Summary
Modified Colitage pink reaction
Answer
A pink reaction using the Modified Colitag presence-absence is most common when testing well water samples containing high levels of iron and or manganese, but specifically iron.

The high amounts of iron can discolor the water sample and the water will appear pinkish-red. The caution with this reaction is that a pink to orange (any yellow color is perceived) could mask the Colitag color reaction of turning yellow for Total Coliforms. But the reaction for E.coli with fluorescence should still occur. If the sample is pink (no perceived yellow) and no fluorescence, then it is a negative result.

Retesting the sample is recommended but if the result is still not conclusive, it is helpful to use another micro media, such as the presumptive test LT or LT with MUG and confirm with BGB for Total Coliforms and/or EC with MUG to confirm for Fecal Coliforms and E. coli.
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