I am using Sodium dichloro-S-triazinetrione tablets to make sanitizing solutions (approximately 200 ppm available chlorine) and disinfecting solutions (approximately 800 ppm available chlorine). Per my understanding and from what I've have read, these solutions do not have a long shelf life and should be replaced within 72 hours.
I am using test strips to validate the strength after mixing and testing each solution daily prior to use. I am storing the solutions in opaque chemical resistant bottles, away from heat and sunlight.
If the readings are ideal for the intended use, is it necessary to discard the unused portion per the recommended guidelines?
I just read your question and it's a good one that chemists encounter frequently. It's really two questions:
1) How stable is the reagent solution, that is, what is the degradation rate under the storage conditions you are using?
2) Do you have a reliable test method for determining active ingredient concentration?
Question 2) would be best answered if you had some independent test method e.g. titration to determine available chlorine. Lacking another method, at least you could establish some sort of calibration curve by deliberately preparing fresh solutions at various concentrations and testing them. I would include some replicates at the key concentrations (e.g. 200 and 800 ppm).
Then, observe their degradation rates over time, which answers question 1). This approach will provide assurance that the solutions you are using contain the required concentraton of chlorine.
Please note: if you are working in a regulated field (or providing materials to clients who are responsible to regulatory authorities), then this qualification process would require significant documentation and a supporting quality system.