Whenever I am in Heroic DM I am having mana problems on Ripsnarl. I did the first time there, but I had just gotten geared for heroics a couple of days prior. Now though I still have problems, especially once the ad phase begins. I initially narrowed it to using DP too much, but even using SW: Pain and MF on ads I still went OOM right as Ripsnarl hit 30%
Is this a common issue? What could I potentially do to fix it?
Its possible to have mana issues on this encounter if you have poor add DPS... the adds double their health pool every 8 sec and will do this on 2 occasions before blowing up. If for some reason you aren't killing adds until they get quite large the amount of spikes you have to cast is double... not to mention the encounter itself goes longer than necessary coz more time is being spent on adds.
Providing you do the encounter properly and have good add DPS then mana should be a non issue. The fact you're having mana problems says to me your group is doing it poorly.