The third tone is in the enharmonic mode (which is microtonally different from the diatonic mode). This is basically a major scale based on γα. There is always (unless otherwise notated) a flat on ζω. The isokratima for this tone is generally on γα.
When applying the third tone to a text, a comma or semicolon in a phrase should end on κε, δι or πα, and sometimes on low νη. A full stop (i.e. period) should end on γα.
The simplified apikhima for this tone is as follows:
γα δι κε δι γα βου πα βου γα
(The apikhima is a mnemonic device which the chanter chants before a hymn written in that tone in order to "get into" the prescribed mode. Other apikhima may be found in Greek and Romanian sources. Many of these can be quite helpful but are not so easily memorized.)