Oscar, I agree with Jesus ...

Oscar,

I agree with Jesus below that equalization may be helpful.  I assume the high is from CIP cleaning with caustic.  Consider isolating that waste stream and pretreat to reduce pH to normal range, then bleed back in.

Also, polyamine flocculants that use a tertiary amine group become non-ionic at high pH which may explain the performance drop at high pH.  Consider jar testing alternative flocculants that are based on quaternary amine groups, which do not lose their charge at high pH.  

Ken Martins