Not to be the bearer of bad news, but I believe that metamagic feats aren't supposed to increase the DC of the spell...with the exception of Heightened Spell:
This is the only metamagic feat that actually increases the spell level (the others require a higher spell slot, but don't increase the spell's level).
You can cast spells as if they were a higher level.
Benefit: A heightened spell has a higher spell level than normal (up to a maximum of 9th level). Unlike other metamagic feats, Heighten Spell actually increases the effective level of the spell that it modifies. All effects dependent on spell level (such as saving throw DCs and ability to penetrate a lesser globe of invulnerability) are calculated according to the heightened level.
Level Increase: The heightened spell is as difficult to prepare and cast as a spell of its effective level.
This is the only metamagic feat that actually increases the spell level (the others require a higher spell slot, but don't increase the spell's level).