It was just the tank glass. As mentioned in the video, the water TDS was maintained in the range of 110 - 130 MicroSiemens (70.4 - 83.2 ppm). IOW, the water was very very clean.The tanks with the most beautiful looking CRS combinations I have seen are in cloudy/milky like waters. That is so odd! I was told "clean" water parameters is key.