TDS is just that Total DISSOLVED Solids, "dissolved" being the operative word. It is the sum of all dissolved charged ions in water, like minerals, salt, nitrites, nitrates, ammonia, etc.
TDS doesn't tell you much without all your other readings. You have Xppm of TDS but what is X? A TDS meter won't tell you that but your other readings do lend some insight.
Since you have such a low TDS and 0 nitrates, ammonia and or phosphates,it only stands to reason, you have low TDS. I expected higher since you have a lot of fish and do feed them and your watershed.
The good news is, your watershed isn't "polluted". The bad news is, your water isn't very fertile.