I think spells like Slow, Haste, ... should have a duration to reduce kiting and to balance the spells. If the player has to cast a spell every few turns the enemy has another chance to resist the spell and the player is not able to do something else. If the duration of the spells scales with the number of shards the effect could be better balanced:

Slow:

Duration: 3 turns + 1 turn per water shard, Effect: Initiative - 5

Haste:

Duration: 3 turns + 1 turn per air shard, Effect: Initiative + 5

Regeneration:

Duration: 3 turns + 1 turn per life shard, Effect: Heals 4 HP, Mana: 10, Life II (Heal should be Life I and should cost 10 mana, too)