It doesn't learn it at a level because it's a tm but it can be teached surf at any level
Chat with our AI personalities
Tentacool will learn Bubblebeam at level 19; Water Pulse at level 33 and Hydro Pump at level 47. You can always teach him the following TM's and HM's: Scald, Rain Dance, Surf, Whirlpool, Dive, Waterfall and Brine.
Most Water Pokemon can learn surf in Ruby, like tentacool or wingull.
Level 25.
You can teach Tentacool the move Waterfall anytime. Waterfall is an HM, not a move gained by reaching a certain level.
Slowpoke does not learn Surf by levelling up, but it can learn Surf via HM in all generations.