I haven't tried seaweed, but Aloe Vera is great for eczema if you're looking for a natural treatment. Aloe has antibacterial properties and a concentrated mix of anti-inflammatory fatty acids and compounds that boost the immune system. I like using the pure gel from the cut stem of the plant, but you can also buy it bottled. It forms a protective layer on broken skin, very soothing and healing. For some DIY aloe recipes and an article on treating eczema check out:
I hope it helps!