Disolve Oxygen levels

[urbanfarmer]

I felt that the discussion of Oliver's article distracted from his post. To be fair I split off the discussion on dissolved oxygen levels. See Aquaponics 101 Part Three: System Design, Continue for the original post...... Badflash
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20% of 240 GPH to jet back is 48 GPH not 40 GPH, but we know what you meant!

Metal isn't intrinsically toxic, but I know you meant that it will reach toxic concentrations with that much metal surface area dissolving into the water. Remember, some people put iron nails and the like into their grow bed to provide the essential trace minerals for the plants, fish, and microorganisms.

The DO is not really helped by air bubbles, per se. You get far more gas exchange at the surface from agitating the water. A simple PVC with many small holes pumping that 20% return water over the surface will give you a ton more DO. Tilapia only need about 4 ppm DO. As far as the growth performance, that depends on so many variables. To say that the growth rate doubled form below 3 ppm DO to 6 ppm DO sounds very misleading. The pH is more important, as considering that low of a DO given the correlation to all the other factors involved, I really question causality you are implying in your statement. Anyway, I digress... Of course, the bubbles will agitate the surface, but I don't recommend spending money on a fancy air pump or air stone when a simple one will yield the same results. Making use of the return water in an efficient way will provide more than enough DO. I understand not wanting a single point of failure. A cheap $20 air pump with a few air stones will be enough to agitate the surface. A water wheel would be the best option, but I'm not sure how much those run these days. Heck, get a 2nd water pump!

So far, this has been my favorite section in the series, lots of practical information here!

[rfeiller]

although it is true that the majority of gas is exchanged at the surface, there is a gas exchange at the bubbles. the finer the bubbles the better. it would be interesting to compare the agitation created by a 20watt air pump verses a 20watt water pump and the resulting DO. since water falling back in from one tank to another would not produce the greatest circulation, the water pump would have to be located at the bottom of the tank pumping straight from the pump outlet and not a hose.

using a power head at the surface, the water stream is weakened by hitting the opposite side of the tank and the circulation of water in the tank is incomplete. the most effective direction is from the floor of the tank at one of the long ends of the container aimed straight up. it will create a complete circulation of the water. you can check this out with dyes added to the water.

[urbanfarmer]

although it is true that the majority of gas is exchanged at the surface, there is a gas exchange at the bubbles. the finer the bubbles the better. it would be interesting to compare the agitation created by a 20watt air pump verses a 20watt water pump and the resulting DO. since water falling back in from one tank to another would not produce the greatest circulation, the water pump would have to be located at the bottom of the tank pumping straight from the pump outlet and not a hose.

using a power head at the surface, the water stream is weakened by hitting the opposite side of the tank and the circulation of water in the tank is incomplete. the most effective direction is from the floor of the tank at one of the long ends of the container aimed straight up. it will create a complete circulation of the water. you can check this out with dyes added to the water.

The DO added by bubbles under the surface, even with the finer bubbles, is crap. I have seen some numbers showing that for the power you get 50x times less gas exchange under the surface. Let me see if I can find that info or paraphrase it (it was in an email from a PhD I was having a conversation with).

[rfeiller]

Read my post again, it is undisputed that the majority of gas exchange is at the surface. When you are maximizing every additional source is valuable. Note the air gap on powerheads to push air into the water jet stream. This was designed for reef tanks for agitation and to add as much oxygen into the crevices of living rock, even tho it was minimal.
I found Badflash's comments on increasing the DO with a column under pressure extremely interesting and I will incorporate the concept in NV as I build there.
Forum's are an exchange of info only to discuss/cuss, accept/reject everything is up for question.

[badflash]

Can you povide a paper or something that supports the idea that bubbles are not as effective as disturbing the surface? I have not found this to be the case myself. I may set up an experiment.

[Oliver]

I need to chime in here, been away since last post, Aquaponics 101 part 4 - system start up.

The older system where the DO measurements were made and reported with increasing DO did NOT have any water being jetted back into the tank. I have built systems like that, however. Regardless of theory and what someone else has written about aerators not providing DO I have the data to prove otherwise, as was given in my original post.

I included water jet back in the "system design" portion of Aquaponics 101; for I have information from others that tell me this is a good way to inject DO into the fish tank water, but again, it was not implemented in the system where I made and reported the DO measurements above.

In the systems I built where the water jet back was part of the system, I measured a DO of over 8.0 ppm. But, there were no fish in that system at the time of measurement; for I was testing a new design and trying to determine how to increase the DO in the water. I still have more testing to do on that system by turning off certain sources of aeration and then testing the DO. Unfortunately, due to some building construction, I had to dismantle the test system before completing all of the DO measurements. I will be resuming those measurements soon and then I will hopefully have a better idea of what elements add DO to the water and how much.

To measure is to know.

[urbanfarmer]

Read my post again, it is undisputed that the majority of gas exchange is at the surface. When you are maximizing every additional source is valuable. Note the air gap on powerheads to push air into the water jet stream. This was designed for reef tanks for agitation and to add as much oxygen into the crevices of living rock, even tho it was minimal.
I found Badflash's comments on increasing the DO with a column under pressure extremely interesting and I will incorporate the concept in NV as I build there.
Forum's are an exchange of info only to discuss/cuss, accept/reject everything is up for question.

Oh, I wasn't disputing you. I just wanted to make that point!

Can you povide a paper or something that supports the idea that bubbles are not as effective as disturbing the surface? I have not found this to be the case myself. I may set up an experiment.

I am not permitted to copy/paste the conversation, but I am allowed to paraphrase. Dr. Wilson Lennard stated that according to research he has access to there is a 50:1 ratio of gas exchange on the surface versus below the surface. I have asked him if I could have access to the research or if it is public. Hopefully, it is something we can all share because I would love to review it as well, but the way he explained it makes sense. The reason bubbles are not HORRIBLE is because although the do not provide much gas exchange in the form of bubbles, it agitates the surface thereby increase the area on the surface as well as adding motion and water movement. I will wait for his response before saying anything else because to be honest this is new to me too. I had no idea the ratio was as high as 50:1 and that is pretty amazing.

Regardless of theory and what someone else has written about aerators not providing DO I have the data to prove otherwise, as was given in my original post.

Can you provide this? I would love to see any of the research you have based many of your claims on!

[urbanfarmer]

This is on YouTube, which is how I heard about the good doc: http://www.youtube.com/watch?v=iitanQgsk2I

Now keep in mind when he did this lecture he was NOT expecting it to be recorded or distributed. Murray Hallam asked him if he could use it, and now it's all over the place, lol

[badflash]

Here is what I would propose. Set up two aquariums. One with a good air stone only, and one with an HOB filter that provides the same mount of surface turbulence. Let it run for 48 hours and measure the DO in both tanks.

Of course the gas exchange occurs at the surface. It has to escape to get away from the water, but I'll get a 6 pack that the DO is better with the air stone than with simple air turbulence. I have tanks with HOB filters, but when I add an air stone the bio load can be pushed more than tripple of the HOB alone.

[jackalope]

I have read that the best way to get higher levels of oxygen in the water is by using a fountain or dropping the water back into the FT from the GBs leaving an air gap of 6 or more inches. If you look at most city reservoirs, this kind of backs up this claim, because they have a fountain in the middle of most reservoirs (and fish ponds in the state fish hatcheries) to add oxygen to the water, rather than air stones. What I read is that the water will not absorb the oxygen molecules from the air being pumped through the stones and up through a water column, as well as it will if the water is picking up oxygen from the air, and forcing it down onto the surface of the water from a fountain or stream (turbulence). These are not my words, ideas or experimentation, I know from nothin' about DO .... some geeky scientist wrote this stuff ... and I'm just quoting it from my bad memory. The water in a creek or river picks up oxygen from turbulence - bubbling brooks and raging rivers with the water running over the rocks and such are a real good example. I can't find it right at hand here, but I have a book on the cichlids (and Tilapia) of Lake Tanganyika and Lake Malawi and it states that in the lower regions of these lakes the fish are more oxygen deprived because there are no currents flowing nor winds blowing the deeper you go - another case for turbulence .

Just my 2 centavos .........