I have a Hanna PH meter that I purchased around a year ago. When I first got it I went ahead and calibrated with the included solutions. For a month or two now I've been having nute problems and could not figure out why. For shits and giggles I measured PH with the strips. The hanna meter was a bit off. I want to recalibrate but I don't have anymore of the solution that came with the kit. Can I use PH up and PH down to do it?
No, you need the solutions. If your in a pinch, you cab create your own, test it with the strips, adjusting it to a pH of 4.0, simulating the 4.0 buffer solution. You'd then calibrate your meter. Problem is, if your off on the pH, then your meter will still read off. I recommend getting more solution.
Color strips aren't that accurate, you should just invest in some solution. Calibration is most accurate with a two point method at 4.0 and 10. Go to your local hydro shop, mine will calibrate anything for free. Once calibrated, and stored properly, it should last for quite awhile...