Is the one extran mama added to the pool only until end of turn or does it keep building turn after turn?
{Darksteel Ingot}
Till the end of the phase.
The mana pool is emptied between phases.
500.4. (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=500.4.): When a step or phase ends, any unused mana left in a player's mana pool empties. This turn-based action doesn't use the stack.