Using depth strider with a merling doesn't stack with the swimming speed it already has but instead acts with the speed of depth strider being basically useless as it's faster having no boots with it.

Wanted to give an add on, I noticed fins don't work properly with dolphin's grace. As when you don't have depth strider you swim faster than without it. But if you have dolphin's grace the swimming speed doesn't increase as much as having depth strider. Fix swimming speed.

Depth Strider works now with Merling's swim speed (since version 0.7.0)