Phytoremediation by potted plants is widely promoted as a low-cost remedy for indoor volatile organic compounds (VOCs), yet the supporting evidence comes from sealed-chamber studies lasting many hours, whereas school-level replications typically use short protocols without leak testing or sensor characterisation. This study (i) built and characterised a low-cost 1 m3 acrylic test chamber, (ii) derived the minimum test duration required for a plant signal to exceed the noise floor of a low-cost metal-oxide semiconductor (MOS) VOC sensor, and (iii) compared first-order VOC decay constants (k) and clean air delivery rates (CADR) of Sansevieria trifasciata, Spathiphyllumwallisii and Epipremnumaureum against empty-chamber and substrate-only controls. Sensor characterisation over 6 h gave a noise standard deviation of 0.151 ppm, a limit of detection (3σ) of 0.453 ppm and a relative detection limit of 9.0%; CO2 tracer decay gave a leak rate of 0.0187 ± 0.0006 h−1 (n = 3, R2 ≥ 0.992). Applying the published CADR distribution of potted plants (median 0.023 m3 h−1) to a first-order model shows that a 30-min test produces a theoretical reduction of only 1.14%, far below the sensor noise floor; at least 4.1 h are needed for a median-performing plant to be detected. Phase III result: one sentence reporting the measured k/CADR ranking and ANOVA outcome from the real experimental data. Failure to detect VOC reduction under short protocols is therefore an artefact of measurement design rather than evidence against phytoremediation. A corrected nine-step protocol with an a priori detectability criterion is provided for school and low-resource laboratories.
