Q. Is a 1% Alconox solution stable in tap water? How long can 1% Alconox be stored as solution? Is pH measurement the best estimate of stability?
A. Alconox is stable in tap water (or any purity water) for at least three weeks when stored in a closed container. The mechanisms of degradation are microbial activity and hydrolysis of the polyphosphates.
We have done studies that demonstrate that under closed lid (only) conditions for three weeks, no microbial growth occurred. However for real life application, the lid will be opened and closed to dispense the 1% Alconox, so you must account for possible microbial growth.
The best way to do that is to monitor the pH of the solution over the course of the three week storage. Take and record a pH start point after initially preparing the solution as a reference point. Typically a drop in pH will detect the onset of microbial proliferation and activity.
Also, another early warning sign of microbial activity is a “characteristic” microbial odor. Monitoring with pH and odor during the three weeks will give you some control to be sure that microbial activity had not started to cause concern. The second possible mechanism is polyphosphate degradation.
Detecting the onset of polyphosphate hydrolysis is a little trickier than detecting microbial growth. Unfortunately the pH only rises slightly as the polyphosphates hydrolyze to ortho-phosphates, and to the best of our knowledge there is no quick and simple way to monitor this.
Though it is in our experience that not a sufficient amount of polyphosphate hydrolysis occurs during the first three weeks to perturb or interfere with performance. So as long as you change the solution every three weeks, there will be little concern other than possible microbial growth.