Double check following.....

1. AC ripples in current  ..
2. Color of film on anode..
3. Analyse film of anode..
4.Contaminated brighner..
5. Unbalanced components of brightner.
6. Quality/ Tracibility of anode lots
7  Cheaper anodes..
8. History of tank solution
9. Lot more reasons...
10.Run lot of HULL cell tests..

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