Unless the ability specifically states that it increases existing swim speeds, than it does not. It gives the character Swim 30 feet, but since the character already has Swim 50 feet, the ability is mostly wasted. However, it might still come in handy if the character loses the natural swim speed, such as when using alter self to appear human, or when baleful polymorphed into a rabbit. The character would retain the Swim 30 feet from their bloodline in that case.
House rule below.
This came up for me before,and we agreed that it wouldn't stack, but to work around it we would have my character take the strong tail alternate and when I reached a 3rd level it just improved the swim speed to 50.
Kept the ability from being useless, but didn't give the full benefit.
|
Unfortunate.
Personally avoided the merfolk when thinking about making an aquatic sorcerer in the past for this reason.(even though the flavor is nice)
Never gotten to play the character yet(and it needs to be recreated after the sheet got deletated) but personally i liked a variation of the Gnome for aquatic sorcerer.
There was something about gnomes living on a artifictal island and having contact with i can't recall if it was aquatic elves or merfolk, but that felt like a fair path of entry.
the swim speed is problably not going to be the only thing your player will get that grant them nothing.
The aquatic bloodline also grant you the "amphibious" label, which the merfolks also have already.
And the Natural armor probably will be wasted as well.
All of these are in the package of the lvl 3 bloodline power, so taking an archtype that replace that power could be an option.
An alternative since it's house ruled, possibly add another +8 to swim checks for the character
Seeker is a good archetype is you want to replace the 3rd level power.
As to other overlapping powers, a merfolk can take the optional racial trait Secret Magic that replaces natural armor and reduces swim speed for a bonus on spell DC's and some SLA's. That way the only "wasted" things are amphibious and swim 30.
I should note that those "wasted" abilities can come in quite handy depending on how your character gets around. For instance, if you use something like alter self for land movement, you'd still have those abilities in that form without having to switch forms. I know from personal experience that a greater hat of disguise makes land exploration a WHOLE lot easier for merfolk that don't have a way to buff land movement [wide tail, travel domain, monk/barbarian fast move, ect].