I just got a TDS meter and the reading on my 33 gallon long, it read 171 which from what I have read seems to be a good number. The only thing that makes me wonder about the level is that I havent done a water change in 2-3 weeks, just top offs with ro water. I havent tested my gh/kh lately, but last time a changed the water it read 0-1kh and 3-4gh. Does this number seem off? What ppm reading should I shoot for? Any help would be great.