Bought a cheap TDS meter and got it today. Tested my tap and it was around 100. My dwarf puffer tank around 160 and my 240 L had 250-260 ppm. The test on the big tank was after a waterchange 50% yesterday and added macros this morning. What are your threshholds for waterchanges? Also, as my plants absorb nutrients in the water column you should see a small decrease in TDS?