This is really interesting! First, I'm amazed at 30 dang feet of pothos!!! LOL- I've got 4 plants coming out of my 75 gallon- pothos and something else I can't remember but saw online that they're good for growing out of a tank. They grow pretty well, but nothing like that- of course, I've only had them in there for 8 months or so.
I've never thought about whether plants take the water and everything else or just what they need, but how would they filter out stuff they don't want? Also, someone mentioned the herbicides, and that's a good point.
To me, it's all in your experience. As has been clearly stated by several, there are so many things one just can't know, so if your experience is showing that your fish are healthy with the regimen you describe over time, then it's working.
However, like many things in the hobby, it is likely a one-off based on the specific conditions you have. It's kind of like planting the same kind of plant in 2 different tanks using the same water, same fertilizer, same water parameters, same lighting and the plant grows like crazy in one tank and will hardly grow at all in the other. Something is different, but Lord knows what it is...
I like changing the water in my tanks (yes, I'm weird), so I'd keep doing it, but hey man, if it's working drive on!
I wonder if the TDS rises as the water level lowers? I know it would from evaporation, but if you could determine how much it would rise from the evaporation and see if you get even more from the rest of the water that is pulled into the plants, then they must be leaving something behind. I guess TDS wouldn't account for everything that's in the water, though.
