Parameters

[IslandReefer]

Because accurate testing is so important, I would buy NEW, for what you can't do without (esp Ca,dKH,salinity and pH) the rest I can or someone can lend you a test kit or meter for (eg. Mg or Cu, TDS pen) if when you need it and don't think you will use it more than once or twice.
IMHO buying used for the first 4 parameters is like buying a used parachute (like new never been opened)or a SCUBA regulator....some do..... BUT!....how attached are you to your reef critters??