Okay so I'm EV training a Tentacool in speed. I equipped it with the power anklet (increases speed EVs by 4) and gave my Greninja the Macho Brace (doubles EVs) and turned the exp share on. Tentacool has Pokerus. Then I went to a route with horde wingulls and used sweet scent with my combee, used surf on the wingulls, and checked the bar. Seems...kinda low. I assumed...

Base 5 EVs from the wingulls.
Macho Brace doubles
Pokerus doubles
Power anklet adds 4

How many EVs should that have given Tentacool?