It's not how it's more when. What i mean i that you wait for the level which 30 so just train hard and it will evolve.
Shellos evolves into Gastrodon at level 30.
Shellos evolves in lvl 30 in a Gastrodon.
Gastrodon
30
lv. 30 platinum
When you level it up to level 30, it will evolve into a Gastrodon.
Shellos evolves at level 30 into Gastrodon. It is the same on Diamond, Pearl and Platinum.
Shellos evolves into Gastrodon at level 30.
Shellos evolves into Gastrodon at level 30.
level 30
evolve shellos or route 218
Level 30.
Gastrodon