highest gas exchange skimmer options

[karimwassef]

I have a local debate on the method that injects the highest volume of air into water.

I'm not concerned with bubble size, etc... just overall air exchange (bubble size is one variable).

The three options being compared:

1. Large volume venturi (like Beckett) using a penductor injector with a high pressure pump. The idea is that fresh air is drawn in through the penductor openings for the highest volume exchange.

2. Large volume bioball column using a tall PVC pipe and high water inlet. The idea is that the high pressure water injection at the top has open air access to draw air in and the large surface of the bioballs creates the greatest opportunity for gas exchange.

3. Large shower head column using a tall PVC pipe and high water inlet.The idea is that multiple streams/jets with a large height can draw in more air.

Other options like needlewheel or air pumps are not in mix because they don't drive very high volume of air... they do create bubbles.

Any of the options above "will work". The question is efficacy in volume injection/air exchange relative to size.

The ultimate design may actually be a combination of the options above - say: recirculating multiple penductor injection jets down onto a high stack of bioballs = recirculating x multiple jets x penductor x bioball stack x height.

Again, the idea is not to create bubbles per-se. So the water level can be very low (unlike a skimmer).

Finally - how would you test it? My proposal is to build all 3 and then measure the volume of air being pulled in using the same water flow pumps.

 

[Annap729]

How might those functions and approaches execute the actual removal of nutrients via foam fractionation? Wondering what the downstream "so then what" looks like from your perspective


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[Annap729]

When you say air exchange, I assume you imply the gas exchange that both oxygenates and process of fractionation? If that is what you mean, measuring orp addresses gas exchange and nutrient testing would be how you'd go about measuring. Additionally, perhaps it would also be of value to measure a per-watt efficiency as well. You may come up with the most amazing way to remove 50% nutrient export at 100watts, but if 30% at 20 watts is the alternative, not sure how valuable this new method of air exchange. Again, just trying to understand the goal of the exercise


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[muttley000]

I enjoy many of the OP's threads! I wonder if the volume of air is less important than the surface area and contact time, therefore making one of the methods you have removed just as likely to achieve the maximum exchange

 

[ca1ore]

I've always been quite skeptical that a skimmer effects much gas exchange. Volume of air injected is absolutely important in primary role skimmer performance, and I'd imagine it probably blows off CO2 as long as the room has a lower partial pressure. I wonder if anyone's actually measured O2 levels pre and post the skimmer. It would surprise me if there was anything more than a negligible improvement.

I've run Beckett skimmers and bioball column skimmers, and subjectively think the former injects more air, assuming similar sizing.

 

[Annap729]

Use Orp probe, unplug skimmer


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[karimwassef]

ok... thanks for the feedback so far

So this is not about foam fractionation.. skimming is the closest thing we do that looks like this, but I'm actually not interested in creating foam for the purpose of nutrient removal at all.

My needle is actually tilting in the direction of nutrient recycling, so export is actually not intended at all.

In terms of primary metric - air exchange: surface area of "fresh" air to water surface is definitely key. So volume of fresh air is a key part of that equation.

Needle wheel and air pump both create bubbles, but I don't see the volume of fresh air being injected. I'll take a moment to consider them - but I hope this doesn't divert the thread:

Air Pump: Unless the plan is to use a single massive blower that does 15 CFM (2 gal per minute), normal air pumps just don't deliver. The 15 CFM blowers are intended for whole stores that are running 100 tanks (100 airstones) or so and can get pretty loud and consume a lot of power. They also need airstones to achieve surface area.

Needlewheel: Very effective at creating bubbles through chopping, but I haven't seen it pulling in large volume of air.

My current skimmer uses only 2 penductors and injects ~ 5 gal of air per minute using water pressure.

 

[Annap729]

What is the purpose of "air" injection in your mind?


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[karimwassef]

In terms of purpose - I wouldn't say it's also CO2 removal or O2 injection... it's actually just air balance with the atmosphere.

This ties into a different thread about CO2 availability since zooxanthelle and algae both consume CO2 for proper functioning and the fact that CO2 is primarily in the form of carbonates in saltwater at reef pH ranges.

If CO2 is high, aeration removes it. If CO2 is low, it injects it. Same with O2.

Why does it matter? balance... The atmosphere (assuming you're not just using air from inside the house or a confined space) is an infinite volume of gas balance - like a stabilizing force that anchors the chemistry of the reef.

In nature, storms, surges, waves, crashing, etc... act as natural forces that continuously regenerate the surface of the water, particularly reefs because they're shallow. In our tanks, we depend on surface area, some aeration and skimming...

I'm not convinced that it's good enough. My current tank was initiated with a massive air exchanger in the form of a monster penductor skimmer and it has survived the unsurvivable... and thrived. I've kept tanks since the 80s and this one has been the most resilient by far. It went through dinos, algaes, massive excursions of both carbonate (kalk disaster 7 to 12) and salt (both extremes - 18 to 45), pH excursions (7.7 to 8.8), power outtages, extreme temps (65 to 90), etc... and still bounces back and thrives (assuming I get the power back on). Even when the power went out, there was no impact for nearly 24hrs of complete still water.

I'm pulling at the threads of why this is because I'm about to tear it down to move.

So, one of the unique elements in my case is the obscene volume of fresh air injected into my water... and I want to tease out what it does through experimentation... and that started a debate with a local reefer about the best (most efficient in terms of space and power consumption) to inject and exchange air.

and that's how we got here.

 

[karimwassef]

I've always been quite skeptical that a skimmer effects much gas exchange. Volume of air injected is absolutely important in primary role skimmer performance, and I'd imagine it probably blows off CO2 as long as the room has a lower partial pressure. I wonder if anyone's actually measured O2 levels pre and post the skimmer. It would surprise me if there was anything more than a negligible improvement.

I've run Beckett skimmers and bioball column skimmers, and subjectively think the former injects more air, assuming similar sizing.

Would you think a Beckett injected at height onto a column of bioballs would do more/less/nothing than the Beckett alone?

 

[Annap729]

Got it. So this has nothing to do with nutrient export (although we do know that O2 exchange is inhibited by higher nitrates).
If the goal is more oxygen in the water (is this your goal?), in order to increase that gas molecule exchange you need more surface area. I think the deeper question you may be asking whether intentionally or unintentionally is whether or not there is a better way to increase water surface area in a given volume water other than foam fractionation (bubble creation). Again, it ties back to what you're trying to do. If the goal is to impart more oxygen exchange, measure the orp. I can push 50 cfm of a gas into a water volume where the surface area is x, but I push 10cfm and the surface area due to my exchange method is >x, which makes more sense? It still leads back to what you want from the air exchange.

Not sure how helpful answering the max cfm question can be if you're not linking it to the surface area calc which is where we see the rubber meeting the road in terms of actual molecule exchange.


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[karimwassef]

I enjoy many of the OP's threads! I wonder if the volume of air is less important than the surface area and contact time, therefore making one of the methods you have removed just as likely to achieve the maximum exchange

thanks muttley. were you thinking of the air pump or needle wheel?

 

[Annap729]

I enjoy many of the OP's threads! I wonder if the volume of air is less important than the surface area and contact time, therefore making one of the methods you have removed just as likely to achieve the maximum exchange

Exactly


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[karimwassef]

Use Orp probe, unplug skimmer


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hmmm. oxidation reduction or Redox is really measuring the outcome, not the forcing function. Maybe oxygen sensors.

 

[karimwassef]

Got it. So this has nothing to do with nutrient export (although we do know that O2 exchange is inhibited by higher nitrates).

So one theory is that nitrates are not intrinsically harmful but their secondary effects on oxygen balance is... In that case, higher exchange would mitigate the effect.

 

[karimwassef]

If the goal is more oxygen in the water (is this your goal?), in order to increase that gas molecule exchange you need more surface area. I think the deeper question you may be asking whether intentionally or unintentionally is whether or not there is a better way to increase water surface area in a given volume water other than foam fractionation (bubble creation). Again, it ties back to what you're trying to do. If the goal is to impart more oxygen exchange, measure the orp. I can push 50 cfm of a gas into a water volume where the surface area is x, but I push 10cfm and the surface area due to my exchange method is >x, which makes more sense? It still leads back to what you want from the air exchange.

Not sure how helpful answering the max cfm question can be if you're not linking it to the surface area calc which is where we see the rubber meeting the road in terms of actual molecule exchange.


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Agreed. I clarified above that it is about air exchange. It's surface area of fresh air to water. Air volume is one part of the formula.

Penductors inherently pull in 4 parts of air for every 1 part of water if sufficient water pressure is applied. So 1/5 of the volume is the forced liquid It's so strong that it can act as a vacuum for the air around the penductor.

This is the theory, but because gas is compressible and liquid is not, I'm not sure what the actual mix rate is.

 

[Annap729]

So one theory is that nitrates are not intrinsically harmful but their secondary effects on oxygen balance is... In that case, higher exchange would mitigate the effect.

I thought that they hinder o2 uptake, and not sure if that's a theory or has been proven.


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[karimwassef]

I thought that they hinder o2 uptake, and not sure if that's a theory or has been proven.


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Think of it as a forcing function with nitrates impeding and higher oxygen availability mitigating that impedance... Like trying to close a door with a stronger gust of air pushing against your force.

 

[Annap729]

Agreed. I clarified above that it is about air exchange. It's surface area of fresh air to water. Air volume is one part of the formula.

Penductors inherently pull in 4 parts of air for every 1 part of water if sufficient water pressure is applied. So 1/5 of the volume is the forced liquid It's so strong that it can act as a vacuum for the air around the penductor.

This is the theory, but because gas is compressible and liquid is not, I'm not sure what the actual mix rate is.

Sure; you may get more cfm, but is it truly separating water molecules in a manner to provide highest exchange?
Again, focusing on cfm is like saying i need a car with a 500 gallon tank but it has one fuel injector versus a 50 gallon tank with the ability to import 8x the usable fuel ( 8 injectors ) v1 vs v8. Capacity versus efficiency.


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[Annap729]

hmmm. oxidation reduction or Redox is really measuring the outcome, not the forcing function. Maybe oxygen sensors.

You can still use an orp probe to determine the impact


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