# Dissolved Oxygen/Aeration - let's get specific...



## hisplaceresort1 (Mar 10, 2014)

Hello again, everyone!
As always, thank you in advance to all that read this and/or take time to reply. It seems like newbies like me have a never-ending stream of questions...

OK - Dissolved Oxygen & Aeration... I recently had a fish die in a small hospital tank while I was treating for fungus. One person told me that I needed to increase aeration while using Pimafix, but unfortunately my little guy had just died... I did have an airstone in there, on full blast, but it might not have been "enough"... I am now having to treat my entire main tank using Pimafix and Melafix. I am currently guilt-ridden that I might have starved my sick fish for oxygen, and now terrified that my tank is not oxygenated/aerated enough.

So... here's what I know about dissolved oxygen (very little). Cooler water holds more. Airstones do not add oxygen to water - only surface tension being broken allows for gas exchange. Some medications reduce it. In Arkansas, our rivers are supposed to have at least 6ppm dissolved oxygen. (Yes, this has nothing to do with a cichlid tank, but at least gives me some point of reference.)

Here's what I want to know:
1.) How much dissolved oxygen is necessary/optimal for cichlids?
2.) I'm assuming some of you buy kits for this... what do you suggest and where do you buy them?
3.) Can you over-oxygenate? How would you know?
4.) Without the benefit of a kit to know for sure, do you think this tank is being oxygenated enough? Too much??? Here's a video so you can see for yourself...

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https://flic.kr/p/mUxC5K

Thanks so much!


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## Deeda (Oct 12, 2012)

I saw your video and in my opinion, that is a lot of water movement and more than I think is necessary. I find that rippling the water surface is usually enough to allow sufficient gas exchange and prevent or reduce any protein buildup that is usually seen from fish food.

I also know that when using Pimafix & Melafix, a bit more than normal aeration is recommended but too much aeration will cause a lot of bubbles forming on the water surface. I think it even recommends it on the instructions, I can't look now because the cat is sleeping on my lap!

A severely over-stocked tank may need the level of aeration in your video because there are more fish competing for oxygen.

This article from the Library offers some information on water movement but doesn't specifically adress how much dissolved oxygen is necessary.


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## hisplaceresort1 (Mar 10, 2014)

Agreed I'm way overstocked; I'm going to have somewhere between a 75 & 125g sooner than later...
That's kind of why I'm hoping to be able to find some real target number to shoot for until I get my bigger tank. 
When I check my water now, I know that 8.2ph is OK, I know that 0 on ammonia and nitrite is necessary, and that my nitrate needs to stay below 20. But for the oxygen, I'm just guessing. And particularly paranoid at the moment...
Thanks for your input. I think I'll tone it down a bit, based on what you said...


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## fmueller (Jan 11, 2004)

The quick answer to your question is that you can measure the dissolved oxygen content of water using a dissolved oxygen meter. Cheaper units may be available, but thankfully measuring oxygen is not necessary for the average cichlid keeper. If you have a good rippling of the surface area of your tank, and/or a good amount of bubbles being blown through the water by way of an airstone, venturi valve, or Durso drainpipe, oxygen will be at saturation levels. This means there will be as much oxygen in the water as the laws of physics allow to be dissolved. Any more oxygen will simply bubble out of the water; meaning you can not over-oxygenate. In my experience it is desirable to have oxygen at saturation levels, especially since this is fairly easy to achieve.

In your tank oxygen is most certainly at saturation levels, and you don't need to worry about it - small tank with spray bar and super vigorous airstone. The mbuna you have in the tank enjoy a strong current, so they likely enjoy that setup. However, less current loving species, or a stressed-out, weaker individual would benefit from the airflow being turned down a notch or three, so they can find a quiet place to rest. Oxygen would likely still be at saturation.



> Airstones do not add oxygen to water - only surface tension being broken allows for gas exchange.


That's a commonly expressed belief in online aquaristic forums. The truth in this is that aeration happens at any surface area where air and water meet. That includes the tank surface as well as the surface of all bubbles. If there is a lot of rippling, and just a few big air bubbles, then the increase in surface area due to rippling will be large compared to the surface area of the bubbles themselves, meaning the contribution to aeration by the bubbles themselves will be small. On the other hand, if you have a very large number of very small air bubbles, their combined surface area could be much larger than that of the tank, and hence they could make the predominant contribution to aeration.

For further ramblings about aeration see my web page on the subject


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## Bikeman48088 (Nov 13, 2013)

hisplaceresort1 said:


> Hello again, everyone!
> As always, thank you in advance to all that read this and/or take time to reply. It seems like newbies like me have a never-ending stream of questions...
> 
> OK - Dissolved Oxygen & Aeration... I recently had a fish die in a small hospital tank while I was treating for fungus. One person told me that I needed to increase aeration while using Pimafix, but unfortunately my little guy had just died... I did have an airstone in there, on full blast, but it might not have been "enough"... I am now having to treat my entire main tank using Pimafix and Melafix. I am currently guilt-ridden that I might have starved my sick fish for oxygen, and now terrified that my tank is not oxygenated/aerated enough.
> ...


Typically, a rule of thumb for estuaries is ~6ppm DO or higher for good fish population health. At 80F, the maximum amount of DO possible is ~8ppm, so you can see that the window is fairly narrow, but is bounded by chemical limitations on the upper end, so it's really impossible to over oxygenate water.


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## hisplaceresort1 (Mar 10, 2014)

Thank you Deeda, fmueller & Bikeman48088. Your input was very helpful, and yes, fmueller - my mbuna really seem to like the current... I appreciate the forum and appreciate your time.


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