old rod can catch what pokemon
Use the Super Rod, and I'll explain why. The Old Rod can catch Feebas, but it also hooks Magikarp and Tentacool, the Super Rod however only hooks Carvanha, therefore making the odds of catching Feebas in the proper tile over 95%. So using the Super Rod boosts your chances by a LOT, and it will make ou work easier. I just checked each tile once with the Super Rod, and when I found the right one, I hooked a Feebas for the first time, so there's no need to fish in each tile about three or four times.