Using a stop alone might be a lengthy procedure with no immediately visible purpose, but using a stop&fix as suggested by Mark will improve BLIX life. Such a stop&fix is dirt cheap and easily mixed from 200 g/l Sodium Thiosulfate, 50 g/l Ammonium Chloride and 20-50 g/l Sodium Metabisulfite (Agfa 304 recipe with optional extra Sodium Metabisulfite). Remember that BLIX rarely runs out of bleaching ability but quickly exhausts its fixer component, so taking away Silver Halide before BLIXing will help a lot.