Kelp is fantastic for all kinds of plants. I haven't used it "indoors" yet, but it's done great things in my back yard.

Well, actually I've used kelp on my indoor plants, but it wasn't pure kelp. I've used a few of Advanced Nutrients products that are made from kelp, Nirvana, Iguana Juice, Mother Earth Tea... there might be others. They're great, but professionally formulated so I can't really compare results with pure kelp added to water.

To the question about the kelp-y taste, I'm a little skeptical. Are you sure it's not your imagination? If not, I'd say it wasn't quite flushed out or you had some residue on the leaves/buds. Kelp is fantastic as a foliar feeding nutrient.