'total dissolved solids' usually in ppm, etc... I got my testers here eBay Store - eSeasonGear: Milwaukee Meters, HANNA Instruments, Meter- Controllers
very good prices, and FAST shipping ... I think i have about $50 or less, invested for both my TDS pen, and pH pen ... you can start with your present lights, but I expect you will be wanting more very soon ... I would use the fluoros for vegging, and get yourself a HPS for flowering ... when thsoe plants get 'bushy', a fluoro just doesn't 'penetrate', that's where ya need the big guns ... now, go read :smokin: