How can you catch the pockemon relicanthe on Pokemon Sapphire?

Search around in the area called sootopolis city in front of the gym on the little island use surf and you will have to go straight down in front of the gym. then you will see a dark castle shape in the water use dive. when your down their you will see a little entrance go through it and you will see grass. Search around in the grass. while searching for it you will meet up on a quite amount of clamperls and chinchou. Keep searching and then you will think you got a plus looking for it after a little while you will meet up on him. i had faith for catching my relicanth.