VIVOSUN Digital pH and TDS Meter Kits, 0.01pH High Accuracy Pen Type pH Meter ± 2% Readout Accuracy 3-in-1 TDS EC Temperature Meter for Hydroponics, Pool and Aquarium, Yellow Blue, UL Certified

Extremely accurate works well it’s a good value for the money the design could be smaller though, and you must recalibrate it every 10 days in order to make sure it stays consistent and must keep the tip in 4.00 ph water or it will dry out and cause false reading

Vivosun Digital pH and TDS Meter receive a 5-star rating because of the customer service, and the products. The pH meter was not working when we received it. I contacted Vivosun and they offered a refund or replacement. I went with the replacement and received a new pH meter the next day. Both meters are working, now I just need to adjust the pH in the water I am giving my herbs so we can all be happy.

It helped me get the pH I wanted for my plants. It appears to be well constructed. I really like how the display lights up upon first use, though I wish it would stay lit because the first several seconds are never accurate, you have to let it calculate and settle for about 60 seconds.Photo is of my pen in my DIY storage solution after 24 hours.WARNINGS FOR ALL NOOBS: Do not trust or test any of these types of products for water resiliency. Do not drop them in water. Only the first 1-1.5in is supposed to ever go into a solution. It shows this on the piece of paper that comes with the product. To avoid contamination do not test directly in your solution. Pour some solution into a small glass to test. STORAGE: as soon as you open up your pen, store your product in electrode solution. If you are not smart: buy a bottle of solution on Amazon. If you are smart you can make your own: buy on Amazon a 1lb bag of KCL, an AMIR portable scale, and some graduated pipettes, and de-ionized water from the grocery store (mine had a machine I had to run to fill up with freshly filtered water). I tested distilled versus reverse osmosis and the RO water was closer to 7.0 so I used this for my solution. Then weigh out and mix 7.45g KCL in 100mL of your neutral water to make 4 molarity (4M) KCL solution. Boom. You now have a lifetime supply of storage solution. I found that through a quick Google Search (Omega Engineering's pH electrode PDF). Pull the pen out of solution, rinse off with a neutral water, put pen in a small glass with 1 inch of solution to test, record value, rinse off with neutral water, place pen back into storage solution.I gave it four stars for several reasons:1) "Very accurate". Meaning, it helps me get closer to the pH I want by increasing accuracy within a 0.1 to 0.5pH range. I don't trust the factory calibration because I have already used it with some variance. I think as soon as you take an electrode out and use it on one source of water you have impaired its ability to test another solution. For analog chemical reagent tests, I have used a general purpose hot tub kit and a General Hydroponics reagent test. It beats the hot tub kit by a huge margin (since that reagent test only tests from 6.8 to 8.2), and the GH reagent kit by a margin of 0.5-0.9pH. E.g. GH was showing 6.5pH, actual 6.2 (with this pen). Then I adjusted pH. GH showed 5.0. Actual was 5.8 (with this pen).2) "Cheap" - can't find anything cheaper.3) It only includes 1 calibration test kit and no reference of where to get more. I would pay $5-$10 more to have a bundle of calibration packets added to my order.4) The display light does not stay on and there is no "light" button.

So I bought this set wanting to try out actually tracking and adjusting my pH and EC of my nutrients for my little indoor hydro-farm. Like most people, I didn't want to spend a lot on my little hobby so I figured I would give this product a try as I actually enjoyed some other Vivosun products.I'll start with the TDS/EC Meter. It is actually decent and appears to be pretty accurate right out of the box. I've used it for a little while and it remains to be acceptably accurate so far without any issues. Good to go, this one I'm pretty happy with and will continue to use at least for now.Next I'm moving on to the problem child, the pH Meter. Wow. Where do I begin. I started off trying to figure out how to calibrate this little thing as the instructions drastically varied from all the calibration videos available online for it. Maybe they changed the method but once I figured out how it wanted to be calibrated I went through the steps and all was good. I tested it a number of times using various testing liquids and it was pretty spot on (at least within acceptable limits for my hobby, not anything that needs to be precise though). So I mixed up some of my nutrient solution, cleaned the pH and TDS meters as advised to in the manual and put them away safely. Fast forward 1 week, I pull out the pH meter and dip it into a cup of distilled water and it tells me that it has a pH of 10.3! Far from the value of 7 I was expecting to see. So I pulled out my other pH balanced liquids to test and every one of them was extremely off from what it should be. It completely lost ALL calibration after one use, and one week of storage. I'm sorry but that means I need to calibrate this thing every time I turn it on? And they only supply you with one set of calibration powder that isn't to be re-used? Absolute and complete garbage. The calibration costs for a year would be well into the hundreds a year for a $10 meter! Absurd. This is a product you should definitely skip buying. Buy yourself a 14-sided dice and give it a roll, it will give you a more accurate guess on your pH level than this thing every will. I would return it, but I was not thinking and threw away the packaging already.

I can honestly say this little pH meter (black Vivosun) has exceeded my expectations. For such a low price point, I figured there would be considerable issues with sensor drift requiring constant calibrations however this little guy has always been within .1 pH when checking prior to the calibrations I have periodically performed over the last few months. Proper rinsing and storage as well as frequency of use are also important factors when maintaining accuracy with a pH meter however the quality of the sensor is also part of the equation. With that being said, this Vivosun pH meter appears to be well made. I would always recommend periodic calibration of a pH meter if you are relying on its accuracy regardless of the manufacturer. The probe is easy to use and easy to rinse after use eliminating any hassles and the removable probe cover provides protection during storage. The readings quickly stabilize which has also streamlined my testing process. Overall, this has been a great value and I would recommend especially if on a budget.