Omg, this is very easy, i take this recipe very early in the game. As you make your dive it is the fourth cave.
1st, is 3 humans
2nd, is a boss that was really difficult when this dungeon began.
3rd, a cave with chests and a similar enemy with the difficult boss, but this one was always easy.
4rth, is the cave you are looking for.
Now there is some black waters before the entrance, try to avoid them. Open the gate, run to the right to the knowledge and exit at once, because this fat guy is very dangerous and if you go solo it is possible to die. All this you can do naked, cary nothing with you. Still to fix the deep water fishing traps, you need dagoon scales. So to farm dagoon scales, the safest way is to go to the first dungeon from the diving side and kill only the minions, not the boss. Then go straight ahead to the last dungeon and fight only the minions again. If you do this 2 or 3 times you will get 20 scales fast and easy. Do not fight the big bosses, it doesn’t worth it, kill only the minions.
One last hint, go to buccaneers bay, to the camp of teimos, kill teimos and take the underwater breathing mask, it would be very handy down there