You should wait 15 min for a reading and use a Calomel reference for Redox measurements.

This is what we do for sediment measurements for wetland soils.
We add CO2 for plants, we can also add O2 gas for the fish to provide a better home for them.

Few have tried this in conjuction with CO2.

A fish health study comparing these and making a CO2/O2 line that signals poor respiration potential for fish/bacteria etc would be nice.


Regards,
Tom Barr