SOS Encounter: Brooklet Hill, Malie Garden
Super Rod: Malie Garden (40%), Brooklet Hill (30%)
Surf: Brooklet Hill (45%), Malie Garden (20%, Only in Ultra Sun & Ultra Moon)
Its base catch rate is 225 out of 255 (higher is easier); the catch rate calculator works out your odds with each ball. For the look, the best colour match is Timer Ball.
Evolution: Goldeen → Seaking (Level 33).
Goldeen in every game · Pokémon Sun, Moon, Ultra Sun & Ultra Moon interactive map (Alola)