Can you catch tentacool in Pokemon platinum with the old rod?

No, you cannot catch Tentacool in Pokémon Platinum with the Old Rod.

Here's why:

* Tentacool is a Water-type Pokémon. In Platinum, Water-type Pokémon found with the Old Rod are limited to:

* Magikarp: Found in most bodies of water.

* Goldeen: Found in some bodies of water.

* Tentacool requires the Good Rod to be fished up in Pokémon Platinum. This rod is obtained much later in the game.

So, if you're looking to catch a Tentacool, make sure you've upgraded to the Good Rod!