underwater sensors

hi, im looking for some sensors to work underwater i want to take care of a fish aquarium, but need to control temperature in the water, and some other contaminants, like methane.... do you know about any kind of sensors for arduino which can work like that??

others I don't know ...

thanks i will see it, thanks fr reply

You can find a lot of air sensors for methane, CO, etc... would it be a legitimate practice to trap the sensors in an air bubble (e.g. inside an upside-down drinking glass) and have that sitting at the surface or underwater?

Or make the sensor part of the filtration system...

Doc

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They are the best I know