Use low charge as a deliberate comparator
A nonionic or low-charge candidate can clarify whether separation depends mainly on molecular bridging rather than strong charge interaction. It is useful beside anionic and cationic candidates when the surface condition is uncertain or changes with upstream treatment.
The label does not make the grade universally tolerant. Molecular architecture, dissolution, suspended-solids concentration and dissolved ions still influence adsorption and floc strength.
Screen beside adjacent ionic profiles
Run equal active-dose curves with consistent preparation and contact energy. Observe initial floc growth, supernatant or filtrate quality, sediment volume and response after a repeatable shear step.
If several products perform similarly in the jar, move the decision to equipment constraints, solution handling, delivered treatment cost and stability across difficult feed.
Document a usable operating window
Retain the lowest stable dose, the overdose boundary and the feed conditions for each result. Repeat fresh-water and recycle-water conditions where ionic strength changes during operation.
The RFQ should include target equipment, water analysis, existing chemicals, required sample quantity and the measurement that will decide acceptance.