Unusually cracked toenails

I can’t seem to fix my cracked toe nails.
They crack right down the middle.
The nails are not yellow or hard.
There is no red or swelling aroung any nail.
They just crack.
It seems to grow out slowly but not completely, just when it is almost grown out, they split again.
Could this be some sort of vitamin deficiency?
It has happened on 3 toes.
I get regular pedicures and my foot health is very good, no itching, blisters or anything else.
Do you have any advice on how to fix this?