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Dissolved Oxygen
http://byap.backyardmagazines.com/forum/viewtopic.php?f=2&t=1947		 Page 1 of 3
Author:  steve [ Aug 8th, '07, 20:15 ]
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Quote:
You CAN def have too much DO. It shows very early in snapper which get bulgy/puffy eyes. Apparently they are kept for this very reason as a canary if u will at the Melbourne Aquarium. If snapper start to get bulging eyes they ease off on the O2.


But is that becasue they are using O2 injection verus AIR ?

Very good info mate, thanks
Author:  EllKayBee [ Aug 8th, '07, 20:25 ]
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Good question Steve, missed that point when I read it...like to know the answer TT :wink:
Author:  twintragics [ Aug 8th, '07, 20:34 ]
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Yep. I guess the commercial guys are whacking the air in and u can have too much of a good thing. So when ur stocking at 60kg per cubic mt of water or more like those guys, things are very knife edge. They need to wack the air in to handle the fish load, but if they have a fubar the margin for error is paper thin. Tough gig, need massive cahones i reckon.

Typically at 20C for example, 10ppm is the saturation point of oxygen in freshwater (at sea level.) Most of our systems would be running around 7ppm in a good setup, 5ppm from pumps with 2ppm contributed by ur biofilter. Silvers will handle 2ppm but need twice that for reasonable growth. Trout need much more say 7 plus, which helps explain why they cark it at temps of 25-28 (higher temp, lower max available oxygen.)

Forgot to mention about the drastic reduction in water DO brought on by feeding. Can drop from 5-6ppm down to 2ppm. For this reason, i now feed my fish a few minutes b4 the pump cycle, so i know DO levels will return to norm, quickly after feeding.

I know most *kittens* this stuff but figure their are a lotta newbies like me and my repeating it here helps me get it in my noggin too!
Author:  rassd71 [ Aug 9th, '07, 09:32 ]
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It may all be 'basic' information, but it's all good!

I didn't realize that you could acutally have too much DO. So, that was good to know. Although with redclaw needing warm water and my elevation being about 4100 feet above sea level, I don't think I can over saturate my water.



As for your keeping going, PLEASE do. I really wish I could take these classes, so THANK YOU for providing the information!
Author:  rassd71 [ Aug 9th, '07, 12:33 ]
Post subject:  Re: Introduction to Aquaculture Course
I've been looking into the numbers for DO and was able to find a couple of good graphs I'd like to share to add to the knowledge base here.

The first one is of the most interest to me, it's about altitude correction for DO saturation...

Image



The other is the temp to ppm

Image

Now, I've been told that it's possible to exceed these numbers and thus 'Super-Saturate' the water... but that will require more research on my part.
Author:  steve [ Aug 9th, '07, 15:10 ]
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rass, i cant understand how altitude would require a correction factor to the MEASURED DO of a water sample.

If its 10mg/l then thats what it is!

Unless they're talking about %DO saturation (from a meter that measures DO and temp and spits out a %)

TT, isn't the line for the mags that you only read the ARTICLES? ;)
Author:  twintragics [ Aug 9th, '07, 18:55 ]
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thanx for the graph rass. I have a few but not quite got the scan/upload thing sorted yet.

Steve, Asio clipped all the articles in my mags so i had to try and glean stuff from the pics.
Author:  rassd71 [ Aug 10th, '07, 09:59 ]
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Here's the clearest explanation I could find...

As altitude increases, the amount of oxygen in a lake or waterbody decreases. This is due to the fact that at higher altitudes, there is less atmospheric pressure available to push oxygen molecules into the water.

It all has to do with the barometric pressure. Water at higher altitude holds less DO. In my case, 4100 feet, it's not that substantial. But it is something to keep in mind.
Author:  Troutman [ Aug 10th, '07, 13:16 ]
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Actually Rassd71 having warmer water means its more likely to get supersaturated with oxygen as it takes far less oxygen to saturate water at warmer temps. Its a common occurence during summer over here in pond culture when abundant aquatic plant growth produces significant amounts of oxygen during sunny weather.
Author:  steve [ Aug 10th, '07, 19:56 ]
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Rass, thats exactly what i mean :) as the altitude inreases the mg/l saturation point will decrease, but if the meter is reading in mg/l then thats what you have in the water ;) corrections should oly need to be made if meter is reading in % saturation

Trout man, is that a bad thing when it happens?

BTW nice fish! how many kgs and what type
Author:  rassd71 [ Aug 11th, '07, 03:17 ]
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While I understand that the plants will produce more oxygen on a sunny day, I was told that the warmer the water, the less DO it's capable of holding. As well at higher altitudes the less it can hold.

As I understand it the meters read the ppm or mg/l of DO. I haven't gotten one yet, it's on my list of things to get.
Author:  twintragics [ Aug 11th, '07, 20:46 ]
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salinity will also reduce DO
Author:  steve [ Aug 11th, '07, 20:50 ]
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twintragics wrote:
salinity will also reduce DO


DO saturation point.

sorry for the correction ;)
Author:  twintragics [ Aug 11th, '07, 21:19 ]
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hmmm, thinking loud here,

salinity and high pH go together (seawater) along with lower DO/saturation point. Would it be fair to say the hydroxyl ions in a high pH solution want to bind with O2 to form sodium hydroxide and therefor reducing available oxygen in the water? (Taking baby steps here, chemistry 101.)
Author:  steve [ Aug 11th, '07, 22:55 ]
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might be a long bow to draw, but i don't really know!
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