Need
"Pandemic" timer :
Agony : 5.4 seconds
Corruption : 4.2 seconds
Siphon Life: 4.5 seconds
Need to fix it, because it's a gain dps more cast "drain soul" with talent "malefic grasp" (+25%) and Proc UA
Ua concept :Wait for your maintenance DoTs to be in pandemic range (<30%).
Refresh your maintenance DoTs.
Unstable Affliction 1-3 times. If you have 1 shard, use it. If you have 2, use both. Try to not spend more than 3 shards per UA cycle.
If you've applied UA 3 times and you still have 4 or more shards, keep applying UAs until you drop to 3 shards. This is to prevent any potential overcapping.
Reap Souls if the Deadwind Harvester buff is down or won't last the full duration of your UAs (usually 6 or less seconds).
Drain Soul until UAs have expired
Preventing Shard capping is always more important than a UA cycle. NEVER HIT 5 SHARDS. If you hit 4 shards you should interrupt your current cycle and dump the UA.