I've been using one for over 2 years now, with no issues. It does ph and tds, stays calibrated, and it works every time. I can replace the ph tip if it ever malfunctions, current cost is $75 on Hanna web site. The total pen price is up to $195 now on the Hanna web site, was $150 when I bought it. If you give your email to the web site, you will get a coupon code for 10% off your first order. That would bring the total down to $175. They are $225 on Amazon.
https://www.hannainst.com/hi98129-ph-ec-tds-tester.html
They also have a less expensive option for a ph only pen (no tds) for $118, replacement tips are $59. This is similar to the BlueLabs Ph pen for $85, so $23 more than Hanna. Not too much more money for the quality. See here:
https://www.hannainst.com/hi98127-phep4-ph-tester.html
Like everyone else, I wasted my money on the cheap pens first. I bought my Hanna after having issues with the other pens and either sending them back for a refund or just tossing them in the trash. The Hanna was a recommendation of a friend of mine who works in a water testing and analysis lab in the municipal water industry. They use Hanna Instruments in the lab which is how he knew the brand reputation (top of the line). If you look on their web site, you'll see what I mean - some really serious equipment. I had never heard of the brand before talking to my friend.
Like any pen, you cannot let the tip dry out or you will have issues. I use the Hanna storage solution in the pen cap when I take a break from growing, usually during the summer June - August. I make sure the cap is full of fluid, then I store the pen in a 64 oz mason jar with a large humidity pack. This keeps the pen tip from drying out. You will see salt migrate out of the pen cap over time while in the jar, once a month I take the pen out, wash off the salt, make sure the cap has fluid, and return it to the jar. I would recommend doing this when storing any brand ph pen, to keep the tip functional.
If you want some even better equipment, these are the ph probes I will buy one day ($400+):
https://www.hannainst.com/search?search_query=99+series+portable#/filter:product_type:Portable$2520Meter/filter:brand:Hanna$2520Instruments
I hope this helps! Good luck.
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