This is just a thought I wanted to add because I've had the hives that you speak of for every year of my life although I'm still not sure what causes it (during allergy season and after fasting).
If chlorella does help remove heavy metals from the body, maybe your body needs help expelling it, and instead of getting removed through your exit point, it's coming out your skin.
The best thing I could suggest to help your body in detox would be sitz bathing. This helps correct the body in expelling toxins through the proper organs so it doesn't have to come out of your skin.
Here's a good article on this from Lapis's Alternative Health blog: