Feebas requires 170 Beauty to evolve.
If blending a Kelpsy Berry with regular NPCs at 100 RPM, you'll end up with blocks with around 23 Dry, thus needing about 8 blocks for a Feebas that's neutral to Dry flavors.
If you blend a Kelpy Berry with the Blend Master, 100 RPM would give you blocks around 51 Dry, needing about 4 blocks to reach 170.