IMO if you are running a tank with CO2 and are adding nutrients such as CSM and K then doing some periodic water changes, even if not every week, is a great help in reducing excess accumulation and/or deficiencies of particular nutrients. Even if you are not following a strict EI regime adding a bit more K than you think you need and then changing water every so often to make sure you don't end up with too much will save you some stress, money on test kits etc. I guess the amount you add is enough but others will probably be able to give a more accurate answer in that respect.

cheers
Neil