LaMotte SMART 2 - Manual (Page 80)

INTERFERENCE: The only interfering substance likely to be encountered in
water is oxidized manganese. The extent of this interference
can be determined by treating a sample with sodium arsenite
to destroy the bromine present so that the degree of
interference can be estimated.
Iodine and chlorine can also interfere, but these are not
normally present unless they have been added as sanitizers.
Bromine - UDV 2/3 Smart2 TEST PROCEDURES 2.04