Reply To: Mayfly Dissolved Oxygen Sensor

I highly recommend the YosemiTech DO sensors, which use optical sensing technology for long-term stability. https://www.yosemitech.com/en/product-cat-11.html

They use Modbus communication and can be user-calibrated. Here are their two main models (the Y505 is new and not on their website).

Y504 (standard model):

~$650 each (plus shipping plus 25% new China import tax)
±1%​ DO accuracy
±0.2°C temp accuracy
5 m standard cable length (10 m at additional cost)
10 s response time

Y505 (low-cost, aquaculture model):

~$450 each (plus shipping plus 25% new China import tax)
±3%​ DO accuracy
±0.5°C temp accuracy
10 m standard cable length
40 s response time
no protection cap over sensor surface

For more info, see https://github.com/EnviroDIY/YosemitechModbus/blob/master/doc/Y50X-DO-ProductProfile.pdf

There are a few minor drawbacks to YosemiTech. They require purchasing with a bank transfer rather than a credit card, and their documentation isn’t great. However, we’re trying to help them with the later by reposting manuals and other info at https://github.com/EnviroDIY/YosemitechModbus. Overall, however, I find their sensors to be of excellent quality, and their email response time to questions (and also a warranty repair) have been quite good.