The alarm was triggered in the early morning, but as expected, did not trigger at the correct water amount. The effect of the tube shifting seems to have a pretty large effect, as it triggered with about 120mL of water remaining (when it should have been 60mL). The scale is pretty sensitive to such small changes, so I'll need to firmly secure the hose so that it does not affect the weight measured.

Some kind of circular, adjustable clamp should do the trick.