It means low salt level (below 2500 ppm). If E91 is shown do the following:
- Test the salt level with a salt test kit. If a salt test kit is not available you can take a sample of the pool water to your local pool supply store. They can test the water for you.
- If the salt level is below 2500 ppm, add only 1.1lbs/0.5kg of salt, at a time, and run the filter until the salt is completely dissolved. If the salt level test is 2500 ppm, then inspect the electrolytic cell for scale build up. Clean it with kitchen grade vinegar as needed. If the above steps do not resolve the error code, contact a Intex Service Center for further assistance.
Note: Always turn the system off and disconnect the power cord before cleaning and servicing.