The method most suited for those without test kits or those with test kits but are too lazy to test is the Estimative Index (EI) that is promoted by Tom Barr. Basically you dose a known concentration of nutrients and every week you do a 50% water change to make sure there are no harmful build up of chemicals. Go to http://www.barrreport.com/forums/showthread.php?t=2062 for the new less technical 'EI-Lite' article or http://www.barrreport.com/forums/showthread.php?t=1 for the in-depth article.