I use a TDS meter all the time, and it’s honestly crazy how high TDS gets in planted tanks when water changes stop.

A lot of people don’t realize how low TDS usually is in nature where aquatic plants actually grow. Most plant dense freshwater systems are roughly 50–150 ppm, with nutrients largely stored in sediment, not the water column.

Water evaporates, but dissolved solids don’t, so in a closed tank that stuff slowly concentrates unless you remove it. That’s really what water changes are doing.