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Ref. No. [UMCES] CBL 2015-014
ACT VS15-07
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Figure 3.
Time series of the Xylem EXO-pH1 test instrument pH results along with the dye reference pH
results for the complete ten week lab test. Results include nine rapid pH transition tests conducted at each
temperature and salinity condition. Detailed plots of each transition test are provided in Appendix I.
The EXO-pH2 also operated continuously throughout the entire lab test and generated
6286 pH measurements at 15 minute intervals (Fig. 4). The total range of pH measured by the
EXO-pH2 was nearly identical at 7.03 to 8.49, and again in close agreement with the range of the
reference pH of 6.943 to 8.502. The EXO-pH2 measurements tracked reference pH similarly
among all water sources and temperature ranges, and consistently responded to the rapid pH
shifts from acid/base additions. The average difference between the EXO-pH2 and reference pH
was 0.04 ±0.10 (N=266), with a total range of -0.31 to 0.19. Initial instrument measurements
conducted with the second seawater trial on the tenth week exhibited a slightly higher offset
(mean difference = 0.17 ±0.003; N=7) compared to measurements from the first week (mean
difference = 0.08 ± 0.007; N=28) (data not shown).