As shown in the figure, attach an active detection cover plate to the main block, run a redstone line to the ME input bus that has a machine control cover plate attached, also attach a machine control cover plate to the other side of the ME input bus, and point a transmitter at it.
Transmitter setting less than value emits redstone signal, label polyaluminum chloride 1000B
me input bin mark 1000b polyaluminium chloride and the amount of ozonated water consumed by the machine each time (when working, look at the main block, it's best to mark the ozonated water value a little bit smaller)