So its my understanding you keep the pen in a cup with storage solution or non de-ionized water. This is supposto keep it from breaking and extending the life of the pen. So every time after use, clean and back into cup of water/solution
I have my pen cap with reference ph 4.0 solution. After I check my water/nutes I just rinse it off with water stick in cap. Every now and then I change the solution. Its ph 4.0 theres no germs at that ph.
I just cut a small piece of sponge and put it in the pen cap to hold moisture, and use storage solution.
depends on the pen. I use Amazon.com: Bluelab pH Pen: Patio, Lawn & Garden SHort term, i just put the cap on it. Long term, placed in tap water. Pretty easy! I also use the ppm pen and love that too!