Feebas does not evolve by level in Pokemon HeartGold. Feebas evolves when it levels up while it has a maximized beauty condition.
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Give it a LOT o' haircuts then level it up.
Feebas will only evolve with high beauty.
In Pokemon Black And White, Feebas will evolve into Milotic by happiness, and, as i recall, berries, this process is easier if it were 'Poke Transfered' from Platinum, Diamond, Pearl, Soul Silver or Heartgold, as you can feed a Feebas Poffins (Beaty) until it won't take anymore. Than you level it up once and it will evolve into Milotic.
you have to max out feebas happines and then level it up one level :DDD
If you get it 8 haircuts/massages and then level it up, it should evolve. Galceon, Leafeon, Megezone, and Probepass must be traded for.