You can conserve your FAS-DPD reagents by using a 10ml pool water sample instead of 25ml. Just multiply drop count by 0.5 instead of 0.2. You can also conserve DPD powder by using one dipper, if the sample turns pink, it's enough.

Are you on Staten Island? I understand sometimes the water near the end of the NYC distribution system can pick up some stuff from the pipes.