Soul Speed doesnt work

I put Soul Speed 3 on my Boots but nothing happened, same speed as always. Tried in creative singleplayer with only soul speed and this also does nothing.

What I expected to happen was...:
A slightly increased speed while running on soul sand

What actually happened was...:

Nothing, just normal walking/ Sprint speed
Steps to Reproduce:

1. Put Souls Speed on your boot
2. Move
3. be faster