Long story short: The tap water TDS = 400, I have access to RO water which i just tested at 0.00 TDS. I also have access to RO run off which TDS = 44. It will be a hassle of time to use the TDS supply. My factual TDS memory is fuzzy so im asking for some help recalling the facts about TDS. WHen I used to grow my tds was about 200 from faucet. You write that number down. Add nutes. The new number is how much nutes you added. Track TDS over the days and see if it raises or lower from plant intake. My question: I've no clue what the other 400 PPM of TDS is. Aren't plants particular about what they absorbed for the most part? Meaning i should worry because the plants will only intake the good nutes i add to the water. Or should i be worried about what's in the tap water and DEFINITELY use RO water since it's available to me at a cost of 1-2 hours everytime i need to refill? ps - TDS = total dissolve solids. RO = reverse osmosis water.