Big Bubbler for pH?

[JimWelsh]

I'll try to explain/remember the air pumped in vs air brought to water surface as is has to do with the volume/concentration of air. Ignore all the incorrect terms as I'm not a chemist.

While chopping the air bubbles into smaller bubbles created more surface area, it does not address the differential concentrations in air exchange. Imagine pumping in x liters of air to mix with the water with the simple assumption is CO2 out, O2 in. The air in the bubble will exchange O2 with the water giving CO2 into that bubble until the concentration of CO2 in the bubble raises. As you add CO2 to the bubble, gas exchange slows, hindering gas exchange. The CO2 in the bubble is trapped until it pops and the higher the CO2 in the bubble, the less effective gas exchange is. Chopping the bubble up just makes this process happen faster, but the limit of say clean air is the air pumped in by the pump, which you can never exceed.

Take that same surface area of water and expose it to your room where the volume of air is so large, the CO2 off gassed by the water will not depreciably effect the O2 in the room without killing you. The theoretical ceiling to gas exchange is much higher due to the volume of air.

This ignores a lot of interactions for simplicity but was the point as I remembered it. Surface Tension in a bubble also had an impact as well with the benefits to a weir vs bubble.

Someone more knowledgeable than me please correct me if I'm wrong, but I'm pretty sure that when it comes to equilibrium between atmospheric CO2 and O2 and dissolved CO2 and O2, the CO2 and O2 are entirely different and unrelated systems. The CO2 should reach equilibrium at the same rate regardless of atmospheric or aqueous O2 concentrations.

People tend to associate CO2 and O2 because of the whole respiration thing, but that link doesn't exist in this context, I'm pretty sure.

 

[Qwiv]

Still confused how you can get to 8.7 unless your corals are growing so fast as to not cause precipitation with CA/ALk. You would need CO2 levels 1/2+ outside air and dHK up in the 10s.

Equilibrium pH Calculator

Aquarium calculator; Estimate the equilibrium pH of your aquarium assuming it is thoroughly aerated.

www.hamzasreef.com

Someone more knowledgeable than me please correct me if I'm wrong, but I'm pretty sure that when it comes to equilibrium between atmospheric CO2 and O2 and dissolved CO2 and O2, the CO2 and O2 are entirely different and unrelated systems. The CO2 should reach equilibrium at the same rate regardless of atmospheric or aqueous O2 concentrations.

People tend to associate CO2 and O2 because of the whole respiration thing, but that link doesn't exist in this context, I'm pretty sure.

No, you are right. Was simplifying so save typing. Would been better to say ratio or something more detailed.

 

[Blaise006]

Sounds like you are taking this approach after doing your homework and have good results, so that’s great. I personally wouldn’t recommend people to aim that high if the goal is just a healthy reef environment with some margin for error as things come up. In my opinion 8.2-8.3 is optimal and going too high or too low are both risky and to be avoided.

But it sounds like your goal is to supercharge stony coral growth, so in that regard and in a very tightly controlled system it may well be better.

The only takeaway I wanted to impart is that I think PH is much more important than given credit for. I aim for a stable thriving reef. I haven’t chased growth rates for atleast a year. I had faster growth at higher alk around 10-11. The monti cap frags that I weighed weekly for 6 months last year had better growth under high alk than high ph in isolation. Higher ph has led to more stability in my experience.

Edit: my experience it is hard for individuals to strip out what it parciptation and growth.

My DKH is 8.2-8.4.

 

[JVU]

Someone more knowledgeable than me please correct me if I'm wrong, but I'm pretty sure that when it comes to equilibrium between atmospheric CO2 and O2 and dissolved CO2 and O2, the CO2 and O2 are entirely different and unrelated systems. The CO2 should reach equilibrium at the same rate regardless of atmospheric or aqueous O2 concentrations.

People tend to associate CO2 and O2 because of the whole respiration thing, but that link doesn't exist in this context, I'm pretty sure.

Correct, the O2 levels don’t impact CO2 diffusion between air and water, and vice versa.

But the absolute quantity difference in CO2 vs O2 in the air (and water) is pretty dramatic- There is about 500 times as much O2 in air as CO2. So a gram of O2 will diffuse into the water much much faster than a gram of CO2 can diffuse out of the water just because the crazy difference in their absolute concentrations.

 

[rygh]

A fun question: What if you made your own air?

1) Completely seal the tank and sump. Actually pretty easy.
Or at least mostly sealed. A few leaks might be a benefit.

2) Put in a CO2 scrubber, that scrubs the entire air in the sealed system.
I would argue this uses LESS media than our skimmer attachment, because after initial removal, it is only
removing the little from respiration in the tank. Currently it always scrubs normal air, which has a lot of CO2.

3) Add a O2 generator. Cheap on amazon, and if they can keep a person alive,
they can certainly deal with a fish tank.


PH should be great. In fact, it might get scary high if you are not careful.
Higher than normal O2 might even help. Who knows.

I started as a joke, but maybe not....

 

[JVU]

A fun question: What if you made your own air?

1) Completely seal the tank and sump. Actually pretty easy.
Or at least mostly sealed. A few leaks might be a benefit.

2) Put in a CO2 scrubber, that scrubs the entire air in the sealed system.
I would argue this uses LESS media than our skimmer attachment, because after initial removal, it is only
removing the little from respiration in the tank. Currently it always scrubs normal air, which has a lot of CO2.

3) Add a O2 generator. Cheap on amazon, and if they can keep a person alive,
they can certainly deal with a fish tank.


PH should be great. In fact, it might get scary high if you are not careful.
Higher than normal O2 might even help. Who knows.

I started as a joke, but maybe not....

#2 is the idea behind recirculating CO2 scrubbers, which draw their air from the skimmer air output in the cup, remove the CO2, then run it as the skimmer air intake.

 

[rygh]

#2 is the idea behind recirculating CO2 scrubbers, which draw their air from the skimmer air output in the cup, remove the CO2, then run it as the skimmer air intake.

So maybe do the entire sump. It has a weir also. And perhaps an airstone.
Might want an air dryer though. That moisture might be terrible for the scrubber.

Actually, I might seriously do that.
Not so much for the tank. But because my sump is in the garage, and my tools are rusting like crazy.

 

[JVU]

So maybe do the entire sump. It has a weir also. And perhaps an airstone.
Might want an air dryer though. That moisture might be terrible for the scrubber.

Actually, I might seriously do that.
Not so much for the tank. But because my sump is in the garage, and my tools are rusting like crazy.

CO2 scrubbers actually do better with high humidity because H2O in the air is required for the chemical reaction that pulls out the CO2 as I recall.

 

[Qwiv]

Where do I subscribe to that build?

 

[Chromis]

The only takeaway I wanted to impart is that I think PH is much more important than given credit for. I aim for a stable thriving reef. I haven’t chased growth rates for atleast a year. I had faster growth at higher alk around 10-11. The monti cap frags that I weighed weekly for 6 months last year had better growth under high alk than high ph in isolation. Higher ph has led to more stability in my experience.

Edit: my experience it is hard for individuals to strip out what it parciptation and growth.

My DKH is 8.2-8.4.

I’m trying to understand what you mean by not chasing growth rates - are you using the high pH to suppress growth or just going for overall health regardless of growth…?

 

[Blaise006]

I’m trying to understand what you mean by not chasing growth rates - are you using the high pH to suppress growth or just going for overall health regardless of growth…?

I implemented it strictly for the health benefits i believe it posed to the system. At higher PH the coral doesn’t need to work as hard to rid itself of the extra hydrogen to deposit skeleton. I believe this reduces stress and increases health. I’ve seen stronger PE and denser skeletons. I can confidently say there are no negatives that I have come across strictly regarding coral health. I do monitor pumps closely for precipitation, but alk and cal are stable and swing less than .2 on average per day. I tested 12 times per day on trident for the first month, then switched to 6 times a day after.

There likely isn’t a big difference in growth rates, IMO, between someone that runs 8.3-8.5 to the 8.5-8.7 that I run given the scale is logarithmic and I don’t want anyone to anchor to that number. I mean that relatively, when the difference in growth rates are compared between the higher levels. When you compare to a system in the 7.8-8.1 range, growth gains are likely much higher.

8.5-8.7 is where this system stabilized for me and it will change with bio load, but my goal is to always keep an elevated PH so that the average of the swing stays above 8.3.

I wanted the take away to be that there may be additional health benefits to coral and that I agree that the metric needs more attention.

I have found growth rates are elevated in both high PH environments and high alk. But when you employ just one of those, alk provided higher weight gains in isolation. If someone were chasing just growth rates I would suggest employing both and be very careful about nutrients. My DKH is 8.2 - 8.4. I didn’t have the space to do a control and i only measured weight gain from monti caps. The higher alk had a less dense skeleton IMO. So maybe the higher weight was from whatever was trapped in the pore structure, like water or tissue. I didn’t find a way to solve that question. Maybe the faster growth was because the montis were use to the environment prior to the test. I understand there were not a lot of variables isolated, but I unfortunately didn’t have the space. Those observations are from an uncontrolled study that I did in my garage, so they ultimately mean nothing, but I figured I’d share regardless.

Edit: I forgot to mention that I found higher alk consumption at the higher PH which led me to believe higher precipitation on surfaces, which makes sense. It never led to an event where alk and cal just started to fall out of solution and cause a white cloud in the tank. Additionally higher PH led to more stable alk tests overall once the higher consumption rate was satisfied.

 

[RandyC]

I have tried air pumps before and though this is unscientific and completely anecdote, I don’t think you’ll see much of a change if you have a tank full of fish and coral with the air pumps. I think you may be underestimating how much co2 is being produced. Don’t forget that coral will be going through respiration at night as well as your fish. And a mature tank full of big coral colonies will produce a significant amount of co2.

I tried briefly on my 6x3’ frag tank in the garage with air pumps. It has a huge surface area and I still wasn’t able to swing the pH with much significance with 2 air pumps and an added skimmer. I think you’d be better off having something that actually used up the co2 in the water. My guess is a big and very well lit (surrounded by light) fuge and a frag tank running opposite cycle of your DT lights will yield better results.

I’m actually trying this in my reefer 250 now. There are actually two light panels on my fuge; one in front and one on the side. The second light panel was turned off for a while, but I turned it back on when I took out the skimmer and added coral frags to the sump. Since doing this, I only see a 0.1 pH swing at night. Before adding the coral in the fuge and turning on the second light panel, my swing was around 0.25-0.3.

View attachment 37652

In case you’re interested, I did this just to see what the effect really was. To the left of the line in the graph, I lit the frags in the sump and the fuge the same hours as the display tank. And to the right, the sump light and fuge light ran opposite the DT light schedule.

 

[JVU]

In case you’re interested, I did this just to see what the effect really was. To the left of the line in the graph, I lit the frags in the sump and the fuge the same hours as the display tank. And to the right, the sump light and fuge light ran opposite the DT light schedule.

View attachment 37703

That’s a great demonstration, thanks

 

[sfsuphysics]

So I did some quick calculations on the side, perhaps poorly, but hopefully not.

Assuming a large ($50 or so) air pump at 20 LPM.
With a 0.5 mm bubble, you have about the same surface area as a 4'x2' tank.
With a 0.05 mm bubble, you have about 10X the surface area as a 4'x2' tank.

Correction if you reduce diameter by factor of 10 total surface area increases by factor of 100

 

[JimWelsh]

Correction if you reduce diameter by factor of 10 total surface area increases by factor of 100

Correction rygh was correct. In each case, we're dealing with the same volume of air ("20 LPM"). The volume of each bubble varies as the cube of the radius, so bubbles 1/10 the size means there will be 1000 times as many of them. But, the surface area varies as the square of the radius, so those bubbles will each have 1/100 the surface area. 1000/100 = 10.

EDIT: His relative proportion is correct, but his calculations for the equivalent tank surface area appear to be way off. 20 liters of air = 20,000,000 mm^3. Bubbles 0.5 mm in diameter would each contain a volume of 4/3*pi*0.25^3 = 6.54E-2 mm^3. 20,000,000 / 6.54E-2 = 3.06E+8 bubbles. Each of those bubbles would have a surface area of 4*pi*0.25^2 = 7.85E-1 mm^2. So, the total surface area would be 3.06E+8 * 7.85E-1 = 2.40E+8 mm^2. There are 92,903.4 mm^2 per ft^2, so the total square footage for the 0.5 mm diameter bubble scenario would be around 2580 square feet -- a lot bigger than a 4'x2' tank!

 

[sfsuphysics]

Correction rygh was correct.

Yup, you (and he) are right, was trying to visualize it in my head with a cube and well needless to say I have a migraine now so that's my excuse for saying what I did and I'm sticking with it!