Nails, weak & dip in the middle

[GingerLemonTea]

Hi,
For over a year now, my thumb nails have been weak with a dip in the middle. I have some strengthening polishes but I'm not sure how often to put these on?
Do you apply daily? Do you remove inbetween applications?

by dip in the middle, do you mean they are spoon shaped? coz if so, you may be anemic. See your GP as you may need iron supplements, or vitamin B or something like that.

Had a google, not really. They are mostly curved like the rest of my nails, but seem to dip towards the end, just the thumbs.