Yeah so any probe with standard BNC connection, such as Digital Aquatics, Pinpoint, Neptune, ect. I'm not sure you'll notice much difference in accuracy between any of them, maybe on lab grade models. For fluid just get same brand as probe, you need a high and low. If your goal is to measure tank pH (~8) then you should buy 7.0 & 10.0. If your goal is measure reactor pH (~6.5) then by 4.0 & 7.0.
Make sense?
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