Swimming pool chemistry: Essentially the same as a coagulant, this chemical (such as alum) is used to combined suspended alkaline material and/or algae into a heavy gel, which sinks to the bottom for vacumning.
Found on http://www.poolsupply360.com/t-Understanding-Swimming-Pool-Terms.aspx
Flocculation is the second step in separation process, where impurities in the water are collected to larger flocculated particles with the aid of flocculant. The flocculant in the water treatment is usually a charged polymer with very high molecular weight. In the flocculation the coagulated particles are bound together and even larger flocculated... Found on https://www.encyclo.co.uk/local/22436