Importance of Dissolved Oxygen?

[Boomer]

There is a field in chemical engineering called mass transfer chemistry and one of thing you will learn form that is the height of the column, mixing rate, internal pressure, dwell /contact rate and flow rate. Flow rate, does not always mean contact time. Meaning, the flow rate form a 4' skimmer can be the same as a 6' skimmer but the contact time/ dwell rate will be different. As you already know bubble diameter is also very important. Don't forget that a skimmers flow rate has two, no one variable, air and water.

Mass Transfer chemistry is a very deep and nasty subject. I'm sure you do not know this but as one approaches the surface of the water, near the water/surface interface, the density decreases and the hydrogen end of the water molecule gets oriented hydrogen end up, something called Surface Relaxation. This increases the activity at the surface, something that may be killed in some skimmers more than others. How much this plays a roll I do not have a clue, it is a new subject in water chemistry and gas transfer rates. Foam Fractionation, how a skimmer works, is a whole field by itself. Randy talks about some it here, although there is nothing on O2.

What is Skimming?
http://reefkeeping.com/issues/2006-08/rhf/index.php


Finally, I think most people have this idea that skimmers or O2 reactors some how do great deeds in O2 enrichment. Well, they don't, you have to ask yourself how much of an increase in O2 in ppm do they elevate it and it is not that much. If you took a well run reef tank, with no skimmer, measured the DO and then added a skimmer, I'll bet the O2 increase will not be much more than 0.5 ppm, if that or say a 10% increase. And 10% is only .5 ppm. Photosynthetic animals/plants will bring about the biggest increase, as they are producing O2 directly. A skimmer is just one of the means to help increase O2.

 

[Herefishyfishy]

Thanks Boomer! So the skimmer doesn't hurt, but a large batch of healthy and growing plants in a well lit fuge appears to be an integral part of the reef tank machine. Also looks like keeping a good wave action in an open tank is an excellent plan.

 

[NaH2O]

The one thing I have a concern about is that folks may not look at the big picture and do research before throwing a refugium on their reef tanks. The recommendation by Eric was use a refugium to help with dissolved oxygen. Well, folks may run out and install a refugium without taking into account the type of macro their going to use and the potential effects. Hopefully, folks that consider adding a refugium specifically for helping with oxygen will look at the pros and cons of the refugium as a whole. Tossing a refugium without research on which macro to use may be a detriment to the system.

 

[Maxx]

Boomer,
Would a an airstone in the sump add as much O2 to a tank as the skimmer or more? How would something like an airstone in the sump compare (O2 sat wise) against a refugium on a reverse daylight schedule? I ask because Eric specifically advocated a refugium and I run a BB tank where an algae based refugium wouldnt work so well.

Nick

 

[Boomer]

Nikki, I agree

Maxx

It depends. Meaning, an airstone turned up so much that the water is "boling" is a nice addtion and alos drives of CO2. But as I mentioined in the other post, there may be salt spray everywhere. What you may want to try in the sump Maxx is a cupped paddle wheel, where the wheel is driven by air under water and the top of the wheel is out of the water. But you do not want it spinning to where it is throwing water everywhere

An airtone in most cases will not out do a skimmer or a good algae growth. The airstone has to many varibles but it is better than notbing. You could also build or buy a O2 reactor. But do not race off and build one like this with out talking to me about it. There are some issue with this simple design that need to be crorected.

http://www.thesea.org/reef_aquarium/DIY/reactors/reactors_o2.php

 

[DonW]

The one thing I have a concern about is that folks may not look at the big picture and do research before throwing a refugium on their reef tanks. The recommendation by Eric was use a refugium to help with dissolved oxygen. Well, folks may run out and install a refugium without taking into account the type of macro their going to use and the potential effects. Hopefully, folks that consider adding a refugium specifically for helping with oxygen will look at the pros and cons of the refugium as a whole. Tossing a refugium without research on which macro to use may be a detriment to the system.

Size is also a issue that never seems to get addressed. Refugiums do a good job but need to be the right size.

Don

 

[Maxx]

Boomer,
I'm was just free thinking when I suggested the airstone...first thought that popped into my head. So what should people who run a BB tank that are unable to grow algae very well, do to provide extra O2 levels at night? Do you feel an O2 reactor is the way to go with that?

Don,
How big should a refugium be ideally (percentage wise) in order to be effective? 20%, 40%, or larger?

Nick

 

[DonW]

Don,
How big should a refugium be ideally (percentage wise) in order to be effective? 20%, 40%, or larger?

Nick

I wish I new. Ive got a skimmerless diehard friend that started with a 30 on his 220 and has moved all the way to a 125 refugium that seems to be doing the trick. I'm sure it will be a 180 pretty soon but his tank is beautiful and BB.

Would be nice if folks would post their before and after ph and or DO levels along with tank and refugium specs.

Don

 

[Scooterman]

Ok here is a simple question, how can I determine If I have an O2 problem & need to do something?

 

[Scooterman]

When I see this and compare it to (see below)

Skimmers are the most efficient means to keep up O2. Plunging water is another one but it will not out compete a good skimmer, unless you want to deal with salt sray everywhere. Air stones do work, they just are not as efficient as say a skimmer. When bubbles are generated and rise to the surface three things happen.

This it almost seems conflicting?? Is a skimmer enough to keep O2 in check?

Finally, I think most people have this idea that skimmers or O2 reactors some how do great deeds in O2 enrichment. Well, they don't, you have to ask yourself how much of an increase in O2 in ppm do they elevate it and it is not that much. If you took a well run reef tank, with no skimmer, measured the DO and then added a skimmer, I'll bet the O2 increase will not be much more than 0.5 ppm, if that or say a 10% increase. And 10% is only .5 ppm. Photosynthetic animals/plants will bring about the biggest increase, as they are producing O2 directly. A skimmer is just one of the means to help increase O2.

Please help the weak minded

 

[Boomer]

No it is not conflicting A skimmer is the best when dealing with equipment, which has been the issue here mostly. But as I tried to indicate there are extremes one can go to that are better at increasing O2, Pure O2 injection, Hydrogen Peroxide drips, peroxide clay reactors etc.. You will be fine with a skimmer, unless you let your tank go to hell.

IMHO most do not need reactors and a good skimmer is fine. I have yet seen O2 levels at dangerous levels, even without skimmers, unless the power goes out. Then you are in trouble with the equipment approach, where that algae will cover your ass for a longer period.

If you want to raise the O2 up a tad, just drop the temp 4F ( 82 -78) and lower the salinity 1 ppt, which will raise it about 0.3 ppm

 

[Scooterman]

Ahh so we're talking only small slight changes like what a good skimmer can do. I don't like playing chemist unless it is necessary, I figure if power fails & my gen. fails I will have bigger problems
Thanks Boomer!

 

[dnjan]

IMHO most do not need reactors and a good skimmer is fine. I have yet seen O2 levels at dangerous levels, even without skimmers, unless the power goes out. Then you are in trouble with the equipment approach, where that algae will cover your ass for a longer period.

But when the lights are off (power goes out), isn 't the algae in the refugium (or wherever) an oxygen consumer?

 

[Boomer]

Yes Don if you left them in the dark. The object would be to not do this

 

[dnjan]

Yes Don if you left them in the dark. The object would be to not do this

I guess that is the problem with power outages - no lights as well. And since many tanks are on inside walls with little or no natural light ...

Seriously - Would a system with plants in the main tank as opposed to a separate refugium be at greater risk (of low oxygen) during a prolonged power outage?

 

[NaH2O]

I guess that is the problem with power outages - no lights as well. And since many tanks are on inside walls with little or no natural light ...

Seriously - Would a system with plants in the main tank as opposed to a separate refugium be at greater risk (of low oxygen) during a prolonged power outage?

I agree, I think it would be worse because the macroalgaes would be taking the oxygen from the main display water. If a refugium is on a separate system, then the water in the refugium wouldn't make it to the main tank, because the pumps aren't working during a power outage. If you have a generator, then it doesn't make a difference because you could work your lights, too, along with your pumps and skimmer (depending on generator size).

On a side note...you could always MacGyver a whole bunch of mirrors to reflect the light shining in the windows over to your tank.

 

[Boomer]

Yes, the refguium would be useless. As far as tank goes, at night of course to a degree during the day not really. How much light is in the room during the day ? Do you turn on lights to see what you are doing ? Do you have plants in the house ? If so, do you aim lights on them ? How many people have house plants that receive only indirect lighting from the outside and still grow ? A friend of mine has a 90 gal tank with goldfish, no lights, no house lights on during the day and no direct sunlight. Last weekend when I was down there you could not even see through the tank glass there was so much algae. Last month the tank walls had been completely cleaned. In a tank with not algae the water would be continuously stripped of O2. In a tank with algae you would still receive some O2 during the day. In a prolonged power outage you may be in trouble, it depends. One really would need to run O2 tests to find out.

Go back to Eric's articles and look at some of the day night light plots. I think there is one there with lights, powerhead and skimmer off. Yes, I know it is not a true indication of a tank with plants vs. no plants. I guess he missed that one and it would have been interesting to see.