How do you evolve Milotic in Gen III-IV?

Question

The Database says "Max Beauty", but do I need to level it up or does it evolve immediately after reaching max beauty?

Answer 1

Feebas evolves into Milotic when leveled up with its Beauty condition high enough in Generation III and IV.

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A Pokémon will have its Beauty condition raised when fed Pokéblocks or Poffins made with Berries that have a dry flavor.

A Feebas's Beauty, when raised to 170 Beauty points or more, will cause it to evolve into Milotic when it is next leveled up.

Answer 2

You have to level it up after its beauty is maxed out.

You have to somehow get its beauty to the maximum and then level it up. After that it should evolve into Milotic.

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Source
Hope I helped.

Answer 3

Right after you max it's beauty in Gen 3 and 4, it will evolve when you level it up. In Gen 5 and 6(excluding ORAS) to evolve feebas you need to trade it holding a prism scale(you can also find Milotic on route 1 via rippling water in Gen 5). In Gen 6 you can trade feebas with the prism scale. In ORAS you can max out its beauty and level it up.
Hope I helped!
Source: Experience