I am not an advocate of using nitrates to judge if the TDS is high..I prefer planted tanks and try to get my tanks to the heavily plantedside. when this happens the nitrates can quickly go to 0 and nitrogen (nitrates ) need to be added..with planted tanks I try to maintain the nitrates btwn 10-20..lucky me the nitrates out of the tap is 20...some say high but in reality the tds is low..I do fairly large changes on all my tanks 30-40% 2-3 X per week..some say too much..
I've been chastised by some on other forums for doing this many large changes as it is stressful on the fish..of course this raises ??? from me..especially in discus tanks where a good water change schedule benefit the discus..of course I usually consider the source (this person raises discus and does 30-40 % once every 7-10 days) . I know from experience that clean water helps the fish..so I'll continue to do 30-40% changes 2-3 X week