Oxygen in water: DO, what's healthy % or ppm?

[pepetj]

I got really lucky and was able to purchase a nice instrument: Oakton DO 300 meter with probe for 60USD (used) and a set of new membranes and electrolyte fluid for another 60USD. That instrument is sold new at 700+USD. It took me a couple of hours to clean the electrodes and it's working.

I also have a Hach O2 test kit but honestly it's a long and complex process to get reliable results (e.g. it needs water to "run" overflowing a bottle for 20 mins before sample is useful so I had to use a small submersible pump to get this done).

This said, as Discus tanks are usually warmer than most other tropical tanks meaning lower values of Dissolve Oxygen should be expected (note: mine are planted with pressurized CO2 in case that needs to be taken in consideration), what would be acceptable levels for Dissolved Oxygen for Discus? Is Bio-available Dissolved Oxygen the same measurement?

I got a readings mostly below 90% DO in one of my Discus tank (after cleaning probe with distilled water I don't have deionized water at the moment).

Thanks for your help clarifying this subject.

Pepetj
Santo Domingo

[Dkarc@Aol.com]

I got really lucky and was able to purchase a nice instrument: Oakton DO 300 meter with probe for 60USD (used) and a set of new membranes and electrolyte fluid for another 60USD. That instrument is sold new at 700+USD. It took me a couple of hours to clean the electrodes and it's working.

I also have a Hach O2 test kit but honestly it's a long and complex process to get reliable results (e.g. it needs water to "run" overflowing a bottle for 20 mins before sample is useful so I had to use a small submersible pump to get this done).

This said, as Discus tanks are usually warmer than most other tropical tanks meaning lower values of Dissolve Oxygen should be expected (note: mine are planted with pressurized CO2 in case that needs to be taken in consideration), what would be acceptable levels for Dissolved Oxygen for Discus? Is Bio-available Dissolved Oxygen the same measurement?

I got a readings mostly below 90% DO in one of my Discus tank (after cleaning probe with distilled water I don't have deionized water at the moment).

Thanks for your help clarifying this subject.

Pepetj
Santo Domingo

Congrats on the meter! Knowing the dissolved oxygen level in your tank(s) is a very valuable piece of information. A minimum "safe" level for most species of fish is 5mg/L. The actual DO saturation point will be dependent upon the temperature and salinity (mostly temperature). Unfortunately, to my knowledge, no one has studied the minimum DO requirement for discus. Given that they are warm water fish, I would guess that the recommended minimum of 5mg/L would be a good starting point. Of course, the higher you are able to maintain it, the better.
The below link should be helpful:

http://www.aquaticeco.com/pages/full...in-Aquaculture

I prefer the measure the DO in actual mg/L, rather than percent saturation. Though 90% saturation is very good, knowing the actual mg/L level is more useful (to me anyways). You will notice that during heavy feedings the DO level will drop as the fishes respiration rate spikes. The key is to be able to maintain the minimum recommended safe levels during heavy feedings. Not only will the fish eat properly, but your biofilter will process the ammonia/nitrite more efficiently as well (bacteria require oxygen too). Of course that leads back to properly designing your aeration system to maintain these levels. Having that DO meter is a powerful tool when growing fish.


-Ryan

[Dkarc@Aol.com]

Also, dont forget to change the membranes regularly!! If you use the meter regularly (several times a week), I would recommend changing the membrane and electrolyte solution atleast once every 2 months. If you use it more frequently (multiple times daily), then I would recommend once a month. Be sure to keep the probe itself clean. Proper maintenance is key for fast and accurate readings. Dont forget to constantly move the probe in the water while taking a measurement. The oxygen levels are measured by consumption across the membrane, so if you keep it still it will slowly deplete the oxygen from the small localized area around the probe, giving you slowly lower readings.

-Ryan