I like Pond Clarifier by Organica. We use it to keep the water really clear in our indoor pond, but it also absorbs ammonia, nitrite, and nitrate (cannot attest to any but nitrate, and that it does lower), and is a Bb. It's fairly expensive, but it lasts a long time. I really hesitate to use "chemicals" (ammo-lock, ammo-zorb, etc,), other than Prime, of course, and this does a good job and you don't have to add it that much after the water is established.