The screen flashing Red/Purple on MMP models or Displaying a Cleaning Notice or Warning on ACE and UCE models indicates that the ionizer wants to do a cleaning.  It means that the next time you ask for water it will clean first for 15 seconds and then it will pour whatever level water was asked for.  The automatic cleaning is based on 2 internal timers, or more accurately a timer and a meter.  There is also a 3rd condition that only affects MMP series ionizers.  It works like this...  

1.) (TIME) If the unit sits unused for 8 hours it will want to clean.

2.) (VOLUME) After 30 liters of water has flowed through the system it will want to clean.

3.) (POWER ON) [MMP ONLY] When MMP series ionizers are first powered on or after loosing power they will always want to do a cleaning.

Because of the time based system virtually everyone sees the cleaning in the morning and in households where everyone leaves the house for 8 or more hours for work or school the unit will want to clean again when it's next used after you get home.  Then you must add that every few days your ionizer will hit the 30 liter mark and it will do an additional cleaning because of that.

The end result is that, depending on use, it is normal for an ionizer to clean between 1 and 3 times in any given day.

If you have doubts about whether your ionizer is behaving as it should the recommended action is to place a pad and pencil beside the unit for at least 3 days and use it to log the times you use the unit as well as every time it performs a cleaning when you go to get water.  You can then compare your log to the above rules.

Final thoughts on self cleaning: The self cleaning feature in your ionizer is there for a reason.  It should not be thought of as a bad thing.  During the normal use of your ionizer the negatively charged plates will attract calcium from that water and this calcium can become stuck to the plates themselves.  Over time this will lead to reduced ionization performance and eventually it can cause the system to clog.  The cleaning works by reversing the polarity of the plates which repels the calcium and produces acidic water which helps dissolve it also.   The cleaner the plates are in your ionizer the more efficiently it will operate and the more hydrogen it will produce.