My smn is running out of mp. Is this a fix?

[Coraliine]

You will still run out of mana using Thunder.

Here are the abilities you should remove from your rotation, in the order that you need:

Miasma II (stop using this if you were using it with contagion, for AoE, it is still OK)
Ruin II (yes, even for off GCDs. If you need to move, just DON'T CAST)
Thunder (yeap)
Shadowflare (at 2+ targets, keep it up still)
Fester (use energy drain instead)

Yup. Miasma II is a complete waste unless you have mana to spare if it's a single target, imo. The time spent running in, and the GCD aren't really worth it if you're tight on mana. However I've never had mana issues when using Thunder.

[pandabearcat]

However I've never had mana issues when using Thunder.

You'll run into problems when you have to thunder adds.

Ruin II is probably one of the biggest mana drains, as it costs you ~65 more mp to save you ~40 (half a ruin) potency worth of attacks, netting you 0.61 potency/mp.

Thunder costs ~228 mp, and gives ~240 potency, netting you 0.95 potency/mp.

Shadowflare costs...ugh, I can't remember, I think 200? mp, nets you ~375 potency, giving you close to 1.875 potency/mp per target, but only if the target is stationary.

Each fester is 300 potency for 0 mp. However, the opportunity cost is energy drain for 150 pp and ~240 mp. 240 mp is 4 ruins, =470 potency.

By dropping fester you gain 170 potency. This is your LAST resort, and generally should never be the case, unless you have ZERO mana and NEED to put up a DoT.