Start with the coagulated solids
An anionic polyelectrolyte frequently works as a flocculant aid after PAC, alum, ferric salt or another primary destabilization step. Record coagulant, dose, pH after addition, rapid-mix energy, delay to polymer and the visible pin-floc condition.
Changing coagulant and polymer together prevents a useful diagnosis. Stabilize the primary stage before comparing polymer profiles.
Use a full dose-response sequence
Prepare all candidates with the same water, stock concentration, maturation and age. Add equal active mass at controlled delay and mixing. Include a blank, the current product, an underdose, several middle points and a deliberate high point.
Observe growth rate, floc size after controlled shear, settling interface, supernatant turbidity, sludge blanket volume and filterability where downstream handling matters.
Watch for residual coagulant effects
Charge reversal after heavy primary coagulation can make an anionic bridge effective, but the response may disappear when raw-water alkalinity or coagulant demand changes. Track pH, conductivity and metal-salt dose with every polymer result.
If the acceptable polymer window is extremely narrow, examine primary coagulation control and injection spacing before requesting a more aggressive grade.
Scale up by sequence, not pump percentage
Transfer the bench order of addition, active dose and mixing logic to the plant. Calibrate both chemical feeds and wait through clarifier residence before assigning a result.
Approve the combination by clarified-water solids or turbidity, sludge handling, chemical mass and process stability. A clear jar at one minute is not enough evidence for continuous service.