Skrelp has Adaptability as one of its abilities, which increases the BAP of moves of its type by 2. Additionally it has Rank 3 SpA vs Slowpoke's Rank 2 SpD so those Sludge Bombs should do 15.5 damage each. Finally 18*1.5=27 not 24. This means Slowpoke takes 99.5 damage over the round and is therefore KOed.