Hi Alex
I don't profess to be an expert on all things co2 yet (only been into this planted tank game for about 2 months now) and I'm sure someone will shoot me down if I'm wrong, but I have learnt that your eyes are the best indicator checker you could ever have instead of comparing it to a label. I have a jbl system and my labels went in the bin after about a week.
When I say this I mean that the general rule of thumb is that
Blue is bad = <30ppm = not enough co2 = slow plant growth and healthy fish
Green/Lime Green is good = approx 30ppm = healthy plants and healthy fish
Yellow is bad = >30ppm = very healthy plants and dead fish
In truth the drop checker is really a pH monitor.
So if this is your first foray into the world of co2 my advice would be to start your co2 dosing slowly (especially if you have fish) and gradually increase your co2 until you get a nice green/lime green colour in your indicator. If you get a yellow colour, you've gone too far so back it off a bit.
One word of advice I would offer you is that you will have to be patient after you make an adjustment to your co2 dosing rate as the indicator can take some 2-3 hours to adjust itself to the correct colour depending on your flow around the tank. Talking of flow, you will now also find yourself tweaking your flow rates and flow directions around your tank too to get an even spread of this valuable commodity we call co2.
This is a great place to get info I have to say, I've gleaned loads of useful info here off of some people that really know this planted tank game and I'm sure they'll add anything if I've missed it (or correct me if I'm wrong).
I think the words 'patient' and 'planted tank' should always be used in the same sentence, they belong together and it becomes a way of life. But worth it in the end.
Good luck.
Chris