fishly Posted December 17, 2003 Share Posted December 17, 2003 Does anyone know how to measure the oxygen level in water? and what is the normal level?Regards,Fishly Link to comment Share on other sites More sharing options...
Adam Posted December 18, 2003 Share Posted December 18, 2003 Well there is a number of ways to measure Dissolved Oxygen (DO). The old fashioned one was to get the sample, add some chemical and then do an end point titration to get the value. Not easy at home unless you have a chemistry set better than most high schools. The next is much easier, thats to buy a DO Meter. They work well if maintained and used properly. The down side is that they cost a bit, particularly the new digital ones, upwards of $600 for a cheap and nasty.The old main stay is to see what your fish and inverts do during the night. If they move to the top of the tank you have low DO levels.DO is measured in parts per million (ppm) and sometimes expressed as a percentage. I personally don't like the percentage as it can give a false sense of security, which I will explain.Theres a few things to remember about how oxygen enters water. It happens most readily at the water air interface. It then has to move from the top to the bottom. Thats why it is possible to have high DO levels in the upper levels and low below. The other point is that the surface tension of most bubbles produced by airstones is to high to allow gas diffusion. The airstones help with aeration by moving water from the bottom to the top. The final point is that hot water holds less oxygen than cool water. For example at around 20oC water can hold 9-10ppm, while at 28oC water only holds 7-8ppm. At temperatures around 30oC it can only hold around 6ppm.Most fish require DO levels above 3ppm for survival, most need it above 5ppm for breeding. No if we have a tank at 30oC that is at 70% saturation, it only has 4.2ppm DO, not high enough for fish to breed.Now the other last thing I'll bore you with is that dissolved oxygen levels will be lowest in the morning when the lights turn on. This is becuase the greatest demand on the DO has occured overnight from the biological (fish and plants) and chemical sources.Hope that helps.Adam Link to comment Share on other sites More sharing options...
bob12369 Posted December 18, 2003 Share Posted December 18, 2003 An easier option is to buy a test kit. I know of one from Sera which is pretty well priced and easy to use IMHO. Link to comment Share on other sites More sharing options...
akroyd Posted December 18, 2003 Share Posted December 18, 2003 Adam,Great reply, thanks for your time and your info. Very much appreciated. Link to comment Share on other sites More sharing options...
Adam Posted December 18, 2003 Share Posted December 18, 2003 Bob,Do you have any more information about the test kit? I didn't know they made them now. I guess their based on the titration method. Adam Link to comment Share on other sites More sharing options...
fishly Posted December 18, 2003 Author Share Posted December 18, 2003 Thanks Adam and Bob. I will try to find out the price of serra DO test kit.Thanks guys, that was a very good article Link to comment Share on other sites More sharing options...
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