CO2 shut off at night...

[smithrc]

Just thought i'd post my findings now that I have set the presurised system back up.

I have been running it again now for about 2 weeks - holding around 35ppm.

I've had a few late nights and early mornigs recently (I'm nocternal) and decided to monitor the PH throught the night to see how much it swung with the CO2 getting turned off with the lights.

I have a KH of about 7 and have adjusted the CO2 to achieve a stable PH of 6.8.

the lights go off at 22:00 as does the CO2 and the PH is stable through the night. for the last 2 nights the PH hasnt swung by more than 0.1

I havent however tested what it swings like with CO2 on all night - but If the plants produce enough to keep the level stable through the night then in theory that would double the co2 in the water leading to quite a large swing.

I'll post the results later as they are on my desktop upstairs.

So from my own experience - I'd reccomend turning it off at night - happier fish and 2x the life from the co2 canister

Has any one else tested?

 

[zig]

Id say gf will be very interested in your results, i know hes going through a....will i....wont i......scenario as regards purchasing a solenoid, personally i think i would buy a solenoid when i go pressurised, after all the plants dont need co2 at night time IMO, but hes more worried about the potiential Ph swings if he runs a solenoid for his beloved discus Digweed.

Ive been doing some research into Ph controllers and the potiential pitfalls with them, so maybe i could post that here as well in this thread, if thats all right with you, im still reading up on them, but i know there are some problems with them.

 

[nodding_dino]

I'd be interested to see what you've found out Zig...

 

[George Farmer]

Interesting thread.

zig is correct - I'm undecided.

Currently I run pressurized 24/7 with only a 0.2 pH swing - 6.5 to 6.7.

My thought is that running a solenoid will in theory save CO2 but in practice may not. When running a solenoid one may have to compensate for the reduced CO2 at night by increasing the CO2 dosing through the day.

Obviously there are many factors to consider i.e. planting, CO2 loss water movement etc.

I would love to be able to just try out the solenoid and test the difference. I may have a word with my LFS.

 

[William]

I do not see why aquatic plants wouldn't take up Carbon dioxide over night. In most natural circumstances, to which these plants have evolved, I'd imagine it's (CO2) the limiting resource and so 24hour uptake of CO2 and storage of it within the plant perhaps as organic acids, until daylight starts and photosynthesis can take place would be desirable, to increase the plants output.

 

[George Farmer]

I do not see why aquatic plants wouldn't take up Carbon dioxide over night. In most natural circumstances, to which these plants have evolved, I'd imagine it's (CO2) the limiting resource and so 24hour uptake of CO2 and storage of it within the plant perhaps as organic acids, until daylight starts and photosynthesis can take place would be desirable, to increase the plants output.

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Hi William, nice to see you contributing to our humble Planted section.

As I understand the photosynthetic process dictates that plants basically consume CO2 and excrete O2 during lighting - consume O2 and excrete CO2 during darkness. But I'm sure you know that already.

Your point is very interesting though and may explain why my plants start pearling literally minutes after my lights come on. I don't imagine they would if CO2 output only started with the lights as it would with a solenoid.

More food for thought - thanks mate.

 

[zig]

I do not see why aquatic plants wouldn't take up Carbon dioxide over night. In most natural circumstances, to which these plants have evolved, I'd imagine it's (CO2) the limiting resource and so 24hour uptake of CO2 and storage of it within the plant perhaps as organic acids, until daylight starts and photosynthesis can take place would be desirable, to increase the plants output.

[snapback]886986[/snapback]​

This has me puzzled, a couple of things on the forum have me thinking and this is one of them (gf will be pleased to know his Ph/Kh crash idea also has me puzzled, but thats not new ive been thinking about that one for a while)

It was my understanding that plants didnt auctually actively take up carbon dioxide but rather it was through passive diffusion through the leaves, or more accurately through the stomata in the leaves and that this only occured during photosynthesis which would occur in nature during daylight hours, and at nightime they would emit carbon dioxide even though co2 would be available to them through the water column. But i wonder at what rate they auctually emit co2 and is there a level at which they stop or will they continue to do so at very low levels until they can photosynthesise again, thats the part that has me wondering.

I think the pearling soon after the lights go on again can be explained by the fact that you are making carbon dioxide available to the plants, and again they are useing this through passive diffusion simply because the co2 is in the water column and they are now oxygenating again.

But regardless of whether i am right or wrong, we do know that plants emit co2 during the respiration phase that happens during lights off, and they are useing the oxygen along with the fish, and it is for this reason that I would switch the co2 off and to prevent any possible toxic buildup.

But there again some aquarists like Lateral Line have had co2 running 24/7 for 15 years with no absolutely no problems, but i am just wondering what auctual benifit it is to the plants if at the same time they are auctually emmitting co2?

Is it only to have the co2 available again for when the lights come on again? but surely this can be achieved by switching the co2 on again via a timer 1 hour beforehand (i know all about Ph swings etc)

Anyway just some useless ramblings, if i have any more i will post them here, or maybe not It got me thinking anyway i guess thats the main point im trying to make.

 

[Walt]

Great useless thinking..
Useless ramblings have solved many questions of the universe...

While plants all perform known traits, i think every tank setup has its differences and whatever works for you, .... ahh... works

Running multiple tanks will show you this....

I think it also shows you that all n all, plants n fish are much more forgiving then we give them credit for....

Another thought... or maybe question....

When injecting co2, it seems we take a kh reading, and i would almost call that a constant.... bear with me...
and that we really 'chase' down the ideal co2 injection rate with the ph...
ie.... 'drive down the ph, to reach 30ppm...and the kh is almost a constant.....

that make any sense?

Could be ive just had too many 13% Golden Belgians too..


That said.... i just added about 1/4 more plants...pumped up my co2 to 70 bpm, and just pulled out 1 of the 2 uprise tubes(UGF) closest to the ladder, and replaced the airstone with a mellow powerhead...pointing behind my 'wall-of-rocks' on the back wall...... this DEFF calmed down the surface distrubance...... should get more co2 into solution, dropping the ph more....

Walt

 

[zig]

When injecting co2, it seems we take a kh reading, and i would almost call that a constant.... bear with me...
and that we really 'chase' down the ideal co2 injection rate with the ph...
ie.... 'drive down the ph, to reach 30ppm...and the kh is almost a constant.....

that make any sense?

The Kh reading is what we "hope" will stay the same, and yes you are correct it is the Ph that we normally follow as our guide to the co2 level given that the Kh should nearly allways remain the same.

 

[Walt]

ok cool....
Thanks for keeping my thoughts straight

its all coming back to me now... after a 10 year hiatus

...ps.. almost up to 20ppm of co2 B)

 

[Angry_Platy]

I have done quite a bit of plant and animal biology in my Science degree. I knew what happens during photosynthesis but forgot the exact components....SOOO....I found this on an easy to understand website :

In the Light Dependent Processes (Light Reactions) light strikes chlorophyll a in such a way as to excite electrons to a higher energy state. In a series of reactions the energy is converted (along an electron transport process) into ATP and NADPH. Water is split in the process, releasing oxygen as a by-product of the reaction. The ATP and NADPH are used to make C-C bonds in the Light Independent Process (Dark Reactions).

In the Light Independent Process, carbon dioxide from the atmosphere (or water for aquatic/marine organisms) is captured and modified by the addition of Hydrogen to form carbohydrates (general formula of carbohydrates is [CH2O]n). The incorporation of carbon dioxide into organic compounds is known as carbon fixation. The energy for this comes from the first phase of the photosynthetic process. Living systems cannot directly utilize light energy, but can, through a complicated series of reactions, convert it into C-C bond energy that can be released by glycolysis and other metabolic processes.

So basically to produce oxygen and to create "pearling" there needs to be light. But adding the second paragraph into the equation says that since in the dark there is stored carbon which, when the lights are turned on is instantly converted into sugars (Carbon-Carbon) bonds.

Clear as mud???

 

[zig]

Clear as mud

 

[Yenko]

Plants emit CO2 at night because they oxidize sugars to provide energy, using aerobic respiration (C6H12O6+6O2 => 6CO2+6H2O).

In Diana Walstad's book, she says that CO2 concentrations are always fairly high in nature, due to the sheer amount of decaying matter at the bottom of most natural bodies of water, so I'm not sure wether the plants would need to store CO2 throughout the night, but I'm pretty sure the fact that they emit CO2 - when logically, the most avaliable source of carbon would be the carbon produced by aerobic respiration is evidence enough that plants do not store carbon at night.

Angry Platy: The light independent processes are not what a plant does at night!

They occur alongside photosynthesis during the light period; however they do not directly use light; just reactants from the Light Depenent Processes. These processes do not occur at night; because the only energy avaliable is stored sugars in the plant; and since the Light Independent Processes create sugar at an energy cost to the plant, there would be a net loss of energy by the plant due to the fact that the processes are not 100% efficient.

 

[William]

Whilst waiting for a clear answer on the mechanisms of aquatic plants, I will just say that, photosynthesis is not homologous with all plants, there are a few variations. Crassulacean acid metabolism plants for example exclusively open their stomata at night and it is during the night that carbon dioxide is fixed into organic acids and stored within the plant and there is no gaseous exchange with the atmosphere during the day the organic acids are simply fed into the oxidative cycle.

I do not see any reason why aquatic plants would not have evolved a CO2 storage mechanism, if CO2 was the limiting factor- however, as Yenko suggests this is not the case, and something else is limiting then obviously they did not reach that hurdle to cross and so didn't

I think as with a lot of things in fishkeeping it's a case for whatever works for you stick with it, and certainly in this case, it looks like switching CO2 off at night is working perfectly so keep up the good work and I look forward to seeing some pictures

 

[Yenko]

Once I get pressurized I'm switching my CO2 off at night; it seems like the only logical thing to do in aquariums with a high plant biomass. In aquariums with little biomass (Many of Takashi Amano's aquariums fall into this category), mabye the rate of CO2 loss from the water would cause an upswing in pH. But, for the majority of us, I think switching CO2 off at night is a good, but not critical step. Although, it might be wise to have the CO2 switch on an hour or two before the lights go on.