Probe needs to be recalibrated monthly according to mfs recomendations, I only got a little amount with the kit so really need some more. I knew that I could get hold of sachets OK but after you calibrate the probe you are supposed to disgard the calibration fluid that you've used. So once you open the sachet and callibrate then thats it gone. I was thinking along the lines of a plastic bottle with the fluid in and only using the amount I needed to just cover the probe tip which would be much more economical.