If this isn’t a digital meter (PH only) then I would strongly suggest you invest in one. I like the Apera meters as do a number of others here.
A TDS meter will be helpful when it comes time to mix nutrients or to perform a runoff or slurry test: inevitable if you are going to grow cannabis.
Another light is good but you might want to look at sending that money into a GOOD light and spend the money once (unlike me lol). Check out this thread: