Not. Regular veg is mostly water & may not have the nutrients your tang requires. Nori is made of porphyra (sp?) seaweed & is a concentrated food. So nutrient levels aside, terrestrial plant foods would mess up your water more because they eat more & poop more.
When they sell top quality dog foods, one of the main selling points is that with really good foods, you'll have very small poops (again with the scientific terminology), whereas with the cheap brands, you'll have much more waste to clean up. It would be similar with feeding fish. High quality, high nutritional value feeds = use less = less poop
Just make sure you buy & feed the unseasoned sushi sheets.
Anthony