Kelp flakes are scratchy. I only use about 1.5 tsp of kelp powder in 59 oz of oils with no overpowering kelpie smell. Kelp needs to be used pretty lightly
All this discussion of stinky kelp makes me think of an experience I had visiting South Korea about 10 years ago. A former student of mine took me to a restaurant than served seaweed dishes and only seaweed dishes. There were dishes made with kelp (brown algae) and dishes made with other seaweeds (red and green algae). They all tasted different. I thought some of them were delicious, but some were. One soup in particular tasted awful to me and was very slimy, but I still ate some of it to be polite . Some seaweeds make or concentrate especially strong smelly marine compounds and others do not. I think that might help to explain why some soap ends up smelling bad and some does not. And while this might be TMI, seaweeds even make odors that help them with with sexual reproduction: https://www.popsci.com/seasmells