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The similarity in performance between the A2 apparatus 5 cm diameter tube settler run with tap water and the A2 same apparatus run with distilled water indicates that calcium carbonate precipitate may not be the main issue. Failure with distilled water suggests that there must be another issue. See the hypotheses page for further information.
Even with the results, one experiment is not enough to reject the carbonates hypothesis. Other factors could affect such as coating of the pH probe with lime particles. Further experiments are required to compare results.