Model 550A, Pro20, and Pro20i Dissolved Oxygen Meter Comparison | YSI

May 30, 2017
The YSI Model 550A dissolved oxygen handheld was an extremely popular meter for YSI customers. Since it's discontinuation we've launched a few models to easily replace the Model 550A with much better benefits. This video compares the Model 550A to its direct replacement - the YSI Pro20i ( - and reviews improvements and features of the Pro20i. The Pro20 ( is also reviewed, although it has a user-replaceable cable unlike the Pro20i and Model 550A.