no filter, no heater, just some moss balls, one plant, one betta. The only light is the dining room table light, which I only turn on when I need it. The betta poops, the plants absorb the ammonia, and I do a 25% water change once a week. The water is crystal clear. No ammonia, no nitrite, 5ppm nitrate. I was skeptical at first but this is the cleanest tank and easiest tank I have.