Red Tint to Black Oxide Holders

We are black oxiding with a proprietary room temp system. We test the chemicals as directed by the manufacturer and change them regularly. In the last two weeks, the process has a rose color over the blacking of the holders. We also have to let the holders set longer before wiping them off. An area on the shank, that is finished ground prior to the is Blotchy. If we wipe it of too soon, the holder is gray instead of black. We prewash the holders in a wash station. Then the holders are dipped in sodium hydroxide for 10 minutes, rinsed in water, dipped in vinegar ⇦in bulk on eBay or Amazon [affil link] for 20 minutes and rinsed in water prior to going on with the rest of the blacking process recommended by the supplier.