Almost every dosing error is a units error. The dose is set in milligrams per litre of water, the pump is bought in litres per hour of solution, and between the two sit a strength and a specific gravity that are easy to apply upside down. This page carries the chain through once — and then answers the two questions a drawing has to answer anyway: what size is the pump, and how often does somebody refill.
The three calculators on this page — dosing rate, day tank storage and the polymer preparation unit — are part of a subscription, along with every design sheet.
The dose is always as the active chemical, not as the solution. A 2 mg/L polymer dose means two grams of polymer per cubic metre, whatever strength it is made up to.
Usable volume, not total. The suction lip, the low-level cut-out and the ullage above high level are not available, and on a small day tank they are a third of it.
Dry polymer is bought by the sack and dosed by the millilitre. The unit wets the powder, then leaves it alone long enough to hydrate — and the sizing question operators actually ask is how often somebody carries a sack up the steps.