Dosing CO2??

[pacificgirl]

How do I do this? I am confused on how this can be done so can anyone explain it to me in a simple manner? I want to try to keep a culture tank (outdoors) of Gracilaria going to feed my tangs and I've heard mention of people "dosing CO2" to increase growth rates I guess??? I have a tank setup and it gets good circulation and tumbling for the Gracilaria, which I also hear is best. Is there an easy way to dose CO2? Like can I add baking soda or something to increase pH or am I totally off here?

Any help is much appreciated! Thanks!

 

[graveyardworm]

The simplest/cheapest method to dose CO2 is with a yeast culture in a sealed container with an airline into the tank. The other method is with a CO2 container, regulator, bubblecounter. Alittle more high tech and costly but dosing is consistant and controllable.

Check with freshwater planted tank stuff for more options. Co2 dosing for saltwater is still in its infancy.

 

[graveyardworm]

Read through this thread for more info.

CO2 Magic

 

[kae]

Is it necessary to dose CO2 in marine planted tank? I've heard that saltwater plants and macroalgae use bicarbonate as their carbon source, not CO2.

 

[Samala]

They can use both forms for their carbon needs. It does not always appear to be necessary to dose CO2, but it can help in tanks with high amounts of plants and no other ready supply of carbonate. It definitely solved my pH problems (well, so long as I remembered to shut it off at night). It also helped with control of nuisance algaes, though that coincided somewhat with better control of nutrients.. which may have helped.

>Sarah

 

[kae]

I've read that most macroalgae mainly use HCO3 but most nuisance algae primarily use CO2. I'm not sure how dosing CO2 can help nuisance algae problem.

 

[graveyardworm]

Dosing the CO2 helps the macros to better utilize available nutrients, and outcompete nuisance type algae.

I think CO2 is more readily available than HCO3. The plant has to work harder to get the C out of HCO3.

 

[kae]

From this article:
http://reefkeeping.com/issues/2006-10/rhf/index.php#2


From this graph, it is clear that if getting carbon dioxide itself is limiting at pH 8.2, it might be more efficient to get it from bicarbonate because so much more is present. In fact, roughly 200 times more bicarbonate than carbon dioxide is present in seawater at pH 8.2.

 

[kae]

And this is what Dr.Randy has mentioned in his Reef Chemistry Quiz 2007.

Unlike many freshwater plant species, which primarily take up CO2 directly, most marine macroalgae can take up bicarbonate ion from seawater in order to get the carbon dioxide that they need for photosynthesis. Consequently, many algae have developed ways of using bicarbonate to gather carbon dioxide. All of these involve somehow combining bicarbonate with a proton to get carbon dioxide.

HCO3- + H+ ----> CO2 + H2O

The various ways that marine algae use this process are detailed in this linked article.

http://reefkeeping.com/issues/2006-10/rhf/index.php#6

 

[pacificgirl]

Wow! Thanks for all of the great info and articles everyone! I will do some serious reading on this and let you know if I have anymore questions.

 

[graveyardworm]

While all of this info is true, CO2 is still easier for the plant to utilize, so if CO2 is present it will be used before the HCO3 is. When CO2 becomes limited the plant then has the ability to switch. The ability to use both is an advantage. The energy costs to the plant are greater if it has to use HCO3, therefore if CO2 is available the plant can devote more energy to growth. Devoting more energy to growth also means more uptake of NO3 and PO4.

 

[Samala]

I'm not going to argue the data or the facts from empirical research. I am reporting only what I observe from my own tank systems.

Systems that are nutrient supplied with no CO2 supplemented: Swings in pH/alkalinity, growth is moderate. It can be hard to favor only macroalgae/seagrass growth over growth of nuisance algaes at the beginning of the life of the tank.

Systems that have both nutrients and CO2 supplemented: Growth is fast to explosive (IME), very little erosion of alkalinity and pH remains stable through the photoperiod so long as CO2 supplementation is shut off at night. Its easier to favor growth of macro/seagrass in these tanks. Its also possible to maintain seagrass under less light when CO2 is supplied.

Again, I'm not arguing the immense carbonate reserves present in seawater. I'm also not arguing that macroalgae take up carbonate for C needs. But, they will also take up CO2 and seagrasses seem to prefer CO2.

If you want to take this a step further I would suggest setting up a tank with nutrient supplementation, and drip in a stream of carbonate to keep your alkalinity stable and the reserves of C stable. See what that does for the plants.

>Sarah

 

[kae]

<a href=showthread.php?s=&postid=10029173#post10029173 target=_blank>Originally posted</a> by Samala
Systems that are nutrient supplied with no CO2 supplemented: Swings in pH/alkalinity.

Systems that have both nutrients and CO2 supplemented: Growth is fast to explosive (IME), very little erosion of alkalinity and pH remains stable through the photoperiod so long as CO2 supplementation is shut off at night.

I don't think that CO2 has anything to do with alkalinity. It affects only pH but not Alk.

 

[3D-Reef]

For the most part Alk is made of carbonates,bicarbonates,carbonic acid/C02.These are always shifting back and forth to stay at an equilibrium.
Buffer(Alk) is made of;
baking soda=carbonate
washing soda=bicaronate
boron=borate
Here's a quote from the same artical.

The carbonic acid that is formed when carbon dioxide hydrates can then very quickly equilibrate into the water's carbonate buffer system, converting into both bicarbonate and carbonate by releasing protons (H+):



The conversions between carbonic acid, bicarbonate and carbonate are much faster than the hydration of carbon dioxide and for most purposes can be considered instantaneous. Consequently, carbonic acid, bicarbonate and carbonate are in equilibrium with each other at any given point in time. The primary factor that determines the relative amount of each species at equilibrium in seawater is the pH, with a small temperature effect as well.

Total Alk will include Ca,Mg,etc..

Ways of dosing C would include;Co2,vinegar,sugar,vodka,seltzer water.Although vinegar,sugar and vodka is in an organic state and may lead to other problems.

I wonder if dripping seltzer water(carbonic acid) would be even easier than Co2?

 

[kae]

<a href=showthread.php?s=&postid=10031607#post10031607 target=_blank>Originally posted</a> by 3D-Reef
.
baking soda=carbonate
washing soda=bicaronate

Baking Soda = Sodium Bicarbonate
Washing Soda = Sodium Carbonate

What is Alkalinity
http://www.advancedaquarist.com/2002/2/chemistry

From it.

Alkalinity Facts

There are several facts about total alkalinity that follow directly from the definition. Unfortunately, some of these have been misunderstood by some hobby authors.

One of these facts is termed The Principle of Conservation of Alkalinity by Pankow ("Aquatic Chemistry Concepts", 1991). He shows mathematically that the total alkalinity of a sample CANNOT be changed by adding or subtracting CO2. Unfortunately, there is an article available on line, which claims otherwise, and encourages people to "lower alkalinity" by adding CO2 in the form of seltzer water. This is simply incorrect.
Forgetting the math for the moment, it is easy to see how this must be the case. If carbonic acid is added to any aqueous sample with a measurable alkalinity, what can happen?
Well, the carbonic acid can release protons by reversing equations 1 and 2:

(5) H2CO3 ==> H+ + HCO3-
(6) HCO3- ==> H+ + CO3--

These protons can go on to reduce alkalinity by combining with something that is in the sample that provides alkalinity (carbonate, bicarbonate, borate, phosphate, etc). However, for every proton that leaves the carbonic acid and reduces alkalinity, a new bicarbonate or carbonate ion is formed that adds to alkalinity, and the net change in total alkalinity is exactly zero. The pH will change, and the speciation of the things contributing to alkalinity will change, but not the total alkalinity.

This is not true for strong acids, however. If you add hydrochloric, sulfuric or phosphoric acids (or any acid with a pKa lower than the carbonic acid endpoint), there will be a reduction in the alkalinity.

 

[Samala]

I did not say that adding CO2 did anything directly to alkalinity.

I have mentioned in several posts here and elsewhere that in an environment where algae/grasses are actively growing that they will find C where possible in a system. That could be available dissolved CO2 from the system itself, or from the carbonates in the alk reserve. My tanks told me that they would consume quite a bit of alkalinity within a day. If you add C in the form of extra CO2, the erosion of alk stops. In the very beginning, and really the whole purpose of my attempt with CO2, was to stop the necessity of adding buffer to the tank on a daily basis. I also noticed that growth was faster when using CO2 than over just putting the alk back in.

By no means am I suggesting that the book is closed on supplementing a C source in a marine planted tank. In fact, I welcome others to experiment and report back.

>Sarah

 

[kae]

<a href=showthread.php?s=&postid=10032377#post10032377 target=_blank>Originally posted</a> by Samala
My tanks told me that they would consume quite a bit of alkalinity within a day. If you add C in the form of extra CO2, the erosion of alk stops. In the very beginning, and really the whole purpose of my attempt with CO2, was to stop the necessity of adding buffer to the tank on a daily basis.

Total alkalinity is not consumed by photosynthesis. Adding CO2 cannot stop the erosion of alk or the necessity of adding buffer to the tank. Marine plants combine bicarbonate with a proton to get carbon dioxide.

HCO3- + H+ ----> CO2 + H2O

HCO3- and H+ decrease together so the Alk stay unchanged.

TA = [HCO3-] + 2[CO3--] + [B(OH)4-] + [OH-] + [Si(OH)3O-] + [MgOH+] + [HPO4--] + 2[PO4---] - [H+]

I think your Alk maybe decrease due to calcification or nitrification process.

 

[Samala]

Adding CO2 cannot stop the erosion of alk

I am not suggesting that adding CO2 does anything for the alkalinity of the system or that it, by itself, does anything to stop the loss of alkalinity that I measured and observed. It does nothing more than give the plants a source of CO2 so that they do not have to follow this pathway of HCO3- + H+ --> CO2 + H20.

Calcification process, doubtful for the system concerned but I'll consider anything. Nitrification, perhaps. I dont know enough about that specific process.

Maybe this comes down to test kits. Mine states that it is measuring carbonate, bicarbonate, borate and hydroxide. Total alk in the pure sense may include all the rest, but maybe that isnt what I'm actually measuring.

>Sarah

 

[Boomer]

Sarah, Kae and others

I was asked to come here for a look.

First, a nice set of posts . Second as far as CO2 addition in seawater aquariums goes it is not an issue of adding CO2 for marine plants. Most marine plants are algaes and don't follow the rule of CO2 uptake that FW plants do. Most macro's do not consume CO2 but HCO3-. However, lower forms of marine algae, usually those not wanted, do consume CO2. The issue behind the CO2 addition is NOT to add CO2 for a C source but to add CO2 to control the pH. And it is actually the main reason for the same in FW. As CO2 leaves the system it causes a shift in the ratio of CO2:HCO3-:CO3. As the CO2 and HCO3- become depleted the pH rises as the reaction shifts to the left. With out the addition of a CO2 source the pH can rise up into 9's. This is at its worse in heavily planted tanks, especially FW and at time in marine planted tanks.

FW has lots of CO2, unlike Seawater which has almost none. NSW only has about 0.40 ppm CO2. If one keeps a higher Alk there will be more CO2 and as the pH drops for 8.3 to say 8.0 the CO2 rises even more.

As are as a reduction in the Alk in planted tanks it is more on the order of the organics the plants give off that reduce that Alk.

Mine states that it is measuring carbonate, bicarbonate, borate and hydroxide. Total Alk in the pure sense may include all the rest, but maybe that isn't what I'm actually measuring.

Yes, that is what TA is. Some kits are then set up to measure components of TA. These are often called P and M Alk , BA and Hydroxide Alk. Hydroxide Alk does not come into play unit the pH is in the 9's. Most tanks that are not being sup'd with Borate will have none, so in a sense the kit's T-Alk is nothing more than a CA kit.

Alk is best looked at as is often used in Limnology books. Alk = ANC (Acid Neutalizing Capactiy). And the more acids a tank puts out the more the ANC/Alk will be depleted.

3D-Reef

I wonder if dripping seltzer water(carbonic acid) would be even easier than Co2?

Yes, it will work and would depend on the demand of the CO2 uptake. Some do use this method. Lets look at the actual CO2 of NSW. As I said NSW has about <.4 ppm CO2, 94 % HCO3 - and 6 & CO3-. If you wanted to keep these ratios, yet raise the CO2 above NSW, just increasing the Alk will do this.

NSW, pH 8.3, Alk 2.25 meq / l = CO2 < .4 ppm

pH 8.3, Alk 4 meq/ l = .67 ppm CO2

If we now just drop that pH to 8.2 = .89 ppm CO2

and if we leave that Alk at 2.25 and drop the pH to 8.2 = .5 ppm CO2

and as this CO2 increases so is there an increase in HCO3 - and CO3--


This all looks like a good discussions and there just appears to be some simple misunderstands in the issues of relationships. What ever system works best for their needs is the one to choose. There is more than one way to skin a cat I might add that one of the worlds foremost FW planted people does not even use CO2, she controls it with more fish = more CO2

 

[3D-Reef]

Thanks for chiming in Boomer!!
I was wondering if You could answer or help Me find out an answer to a simliar question?A little back ground first.My grass tank is hooked in with My DT.In the DT I have a mix of corals,sps,softies,ect..They say sps need a Ph of 8.2/or higher for calcifcation.
The problem comes when I try to maintain a High Ph by useing kalk or if I add sand to the DSB,I get a white deposit on the fronds of the grass,the side closest to the light.
Do You think dosing Co2 would help in stopping this?I otta add the fuge is large and on reverse daylight.