This disclosure relates to early detection of low bicarbonate level. In certain aspects, a method includes receiving a first signal from a conductivity detector connected to a line through which a solution of salt concentrate and fluid flows and determining a first conductivity of the solution based on the first signal. The method also includes receiving a second signal from the conductivity detector at a time after receiving the first signal, determining a second conductivity of the solution based on the second signal, and determining whether the second conductivity is less than the first conductivity by at least a threshold amount.