Yellow Treat®, No Mor Problems® (Mk.I Formula), Pink Treat®
Immediately after a rescue treatment, chlorine readings are extremely low or non-existent.
On occasion, the bromine in the algaecides can interfere with the test reagent to give a false zero chlorine reading. This is due to bromine acting as a reducing agent on chlorine, preventing the reaction of the reagent. It's important to remember that although your test can't see the chlorine, the chlorine is still working in the water. In fact, the same reaction is actually accelerating or "super-charging" the chlorine. Note: This issue was resolved in the Third Generation of United Chemical algaecides (No Mor Problems® mk.II , Swamp Treat™).
Use an OTO test: Using an OTO test will give better results versus a DPD test. The OTO test is less susceptible to the issue.
Let the Test Stand for 5 minutes: Letting the test stand for approximately 5 minutes helps yield a reaction where a chlorine reading will be visible.
Chlorinate as Usual: Chlorinate as usual and the problem will often subside in approx. 1-2 weeks. Shocking can actually exacerbate the problem. As long as your pool is clean, your chlorine is working.
Test before using algaecide: Testing before adding the affected algaecides will help ensure you have a more accurate test result.