# Oxygen diffuser in reverse cycle off c02/lighting period - why wouldnt you...



## Paul Kettless (11 Feb 2021)

Hi all,

After reading @Leah95 post earlier, it was discussed in there about the importance of surface agitation and gas exchange, and a very helpful video posted to view.  This has lead me to some late night reading/watching on the subject and I am very new to c02 injection so this is all a steep learning curve.  Therefore, it lead me to the video below, and also a couple of articles that suggested that simple agitation from a canister filter is most probably not enough when c02 off, lights out and plants have stopped photo synthesis. It suggested the c02 20-40ppm average, but also Oxygen 7-10ppm. Firstly, how can anyone test that? My understanding is that the equipment is very expensive.

I dont seem to see many people doing this, and I guess its why I am making this thread. Is there any benefit to running an oxygen diffuser/airstone in reverse of the lights/c02. Its seems quite logical but there must be reasons why it not favoured by many.  Surely its not just aesthetics and people dont want to see yet another piece of equipment and pipe in the tank.  I have looked in the archives and there are some very advanced conversations about dissolved oxygen, but the reading goes way above my head and leaves me even more confused than before I started.  Ive put one of the videos below, and would appreciate your thoughts.


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## Sammy Islam (11 Feb 2021)

Aesthetics aside, maybe in an open top tank there would be too much splashing outside the tank depending on water height and pump strength?

Some people raise their lily pipes for extra surface agitation/02 exchange. Personally i do increase surface agitation at night by angling the lily pipe upwards by wedging a sponge between the pipe and tank.


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## Leah95 (11 Feb 2021)

Hi Paul!

Something I forgot to mention in my updated post was that I currently use an airstone every other night. I turn it on when the lights go off at 10pm and turn it off when I wake up in the morning around 8am. I’ve personally had a really good experience with it!

As a newbie, the first few weeks of the setup there was a lot of plant decay and biofilm/surface scum present. This was mainly due to my lack of knowledge but also attempting to get the co2/dosing/parameters right. I noticed my oxygen levels were fluctuating a lot - fish lethargic but not gasping and I also tested levels with the test kit (I had 3 fish leftover from a previous tank so oxygen was really important - I didn’t have anywhere else to store them). I believe the thick surface scum caused by a lack of flow and lots of decay wasn’t allowing a good enough gas exchange to happen so the co2 wasn’t getting out and the o2 getting in. I initially added the duckbill outlet to my stock pump which didn’t break the water but dramatically increased the flow (from what I can see), however, at one point the scum was so thick even the flow wouldn’t break it. I’d read somewhere about the air stones, someone said they’re really good at night, especially for a new establishing tank as it adds additional oxygen which may be taken up by the bacteria/algae/fungus that occurs at the start of a set up - this made logical sense to me. The post also said it’s great for the plants and fish at night and helps gas exchange obviously with the bubbles bursting at the surface.

I tried this and the next day there was zero surface scum, my water was crystal clear. It also got my drop checker to turn blue (it was initially staying green 24/7 even though I knew the injected amount was right. The fluid wasn’t faulty so I knew it had to be something to do with the gas exchange). My fish also seemed a lot more active. I checked my o2 levels before and after and I checked them daily for a week and they’ve stayed in a good range (I used the JBL Oxygen test kit, I know the tests are not 100% accurate but they give a decent enough reading). I haven’t noticed it affect my co2 output, I’m currently at 2bps 2hrs before lights which gets my drop checker green before they come on. I did have to increase it from 1bps when I added the outlet.

I will personally use the airstone until I feel my tank is at a stable stage where I’ve found the balance between light/nutrients/co2 - essentially until my plants stop decaying and have healthy leaves haha. I’ve personally had good experiences with the airstone and I’d probably recommend it to another newbie who’s still in the process of finding the right tank balance. I guess those who are a little more familiar with planted tanks don’t use them because they don’t have a lot of plant decay/biofilm on the surface, just a theory however! Also, aesthetic-wise, I just take it out in the morning, stick it in a bucket behind the tank.

I’ll be following this post to see what others say as it wasn’t until someone posted about flow/gas-exchange that I became aware of it


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## dw1305 (11 Feb 2021)

Hi all, 


Leah95 said:


> ..... I’ve personally had good experiences with the airstone .....





Paul Kettless said:


> ..............................and also a couple of articles that suggested that simple agitation from a canister filter is most probably not enough when c02 off, lights out and plants have stopped photo synthesis..................


I like extra aeration, realistically you can never have  too much oxygen.  Have a look at <"Aeration and dissolved oxygen....."> I wrote it specifically for <"Plec keepers">, but it is relevant to all fish keeping.

On UKAPS <"Oxygenation via plants"> and <"@Geoffrey Rea 's post">. would be useful,  I think Geoff measured oxygen levels over night as well <"with a DO meter">. 


Paul Kettless said:


> Firstly, how can anyone test that? My understanding is that the equipment is very expensive.


Unfortunately the meters are expensive, but we have some people <"who have tried them">.

What a lot of people don't realise is that when plants are photosynthesising <"their internal tissues"> become <"filled with oxygen"> and it is that oxygen that the plants largely use at night. 

cheers Darrel


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## Dr Mike Oxgreen (11 Feb 2021)

These days I run an air pump and stone overnight on a timer, switching off at the same time as the CO₂ starts, a couple of hours before lights on. I think my ember tetras are more active and less timid than they were prior to using aeration.


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## john dory (11 Feb 2021)

Thing that puzzles me is...Naturally,co2 would be increasing during the night.


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## john dory (11 Feb 2021)

My plants are"awake"long before my photo period starts....but there's no co2!
This wouldn't happen naturally.
Those early risers would get first dibs on the co2 that had accumulated during darkness.


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## Paul Kettless (11 Feb 2021)

Leah95 said:


> Something I forgot to mention in my updated post was that I currently use an airstone every other night. I turn it on when the lights go off at 10pm and turn it off when I wake up in the morning around 8am. I’ve personally had a really good experience with it!


Pleased to hear that, and from the reading that I have been doing it seems to suggest that the benefits are not just for newly established tanks


dw1305 said:


> I like extra aeration, realistically you can never have too much oxygen. Have a look at <"Aeration and dissolved oxygen....."> I wrote it specifically for <"Plec keepers">, but it is relevant to all fish keeping.


Very good read that article Darrel, Kudos to you sir for that. Although I will admit some of it went straight over my head....


john dory said:


> Thing that puzzles me is...Naturally,co2 would be increasing during the night.


Maybe my poor learning here, but I thought it was the other way round and the levels fall?

If the agitation is not enough and elevated levels of c02 remain in the system, Im assuming that this could lead to possible problems for our fish, and maybe more so shrimp as I understand they have a lower tolerance to higher c02 levels.  I would have thought that once c02 stops, getting the equilibrium back to a normal level as soon as possible would have benefits to the fish, and I guess this is depending on the agitation and gas exchange.

It seems like adjusting the outflow of the lily pipe to give more surface agitation before bed would possibly help some.


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## Sammy Islam (11 Feb 2021)

Paul Kettless said:


> Pleased to hear that, and from the reading that I have been doing it seems to suggest that the benefits are not just for newly established tanks
> 
> Very good read that article Darrel, Kudos to you sir for that. Although I will admit some of it went straight over my head....
> 
> ...


I find that my tank degasses the CO2 i have injected in about 1.5 hours without having to angle my lily pipe upwards. I only angle the lily upwards before i go to bed.


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## Paul Kettless (11 Feb 2021)

Sammy Islam said:


> I find that my tank degasses the CO2 i have injected in about 1.5 hours without having to angle my lily pipe upwards. I only angle the lily upwards before i go to bed.



Interesting, so you clearly have good gas exchange on your system in place.


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## dw1305 (11 Feb 2021)

Hi all,


Paul Kettless said:


> Very good read that article Darrel, Kudos to you sir for that.


Yes, it wasn't as well received as I'd hoped at the time, but I think more people have probably come around to it over the ~15 years since I wrote it. I stand by it as a document, although in many ways <"the past is a different country">.


Paul Kettless said:


> Maybe my poor learning here, but I thought it was the other way round and the levels fall?


It is just the difference between "added CO2" and "no added CO2" tanks. 

In a "High tech" CO2 levels will fall as the excess CO2 outgases to the atmosphere and your drop checker will change back to blue. Once CO2 is at atmospheric equilibrium values levels may then rise again as the bioload respires (while you don't have any photosynthesis).

In a "Low tech" you don't ever have that excess of CO2, its level will track atmospheric levels and they will rise at night, due to respiration.

In both cases the level of night time CO2 will depend on the gas exchange surface area and bioload.  So if you have a lot of fish and no circulation you run the risk of your fish asphyxiating during the night. If you don't have plants it is "always night".

cheers Darrel


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## Nick potts (11 Feb 2021)

Sammy Islam said:


> Aesthetics aside, maybe in an open top tank there would be too much splashing outside the tank depending on water height and pump strength?
> 
> Some people raise their lily pipes for extra surface agitation/02 exchange. Personally i do increase surface agitation at night by angling the lily pipe upwards by wedging a sponge between the pipe and tank.


I recently started using an airstone at night as I was suffering from cyano, the tank is small and open-topped, as a result, the lights and most stuff surrounding the tank was misted with water constantly, that was enough for me to stop and just angle my spray bar a bit more.


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## john dory (12 Feb 2021)

dw1305 said:


> It is just the difference between "added CO2" and "no added CO2" tanks.


I was thinking more about what happens in the natural habitat.
Wonder what the co2 profile would be any plant....let's say blyxa...where it occurs naturally.


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## john dory (12 Feb 2021)

Should probably start another thread.
Apologies to the o.p.


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## dcurzon (12 Feb 2021)

ive often wondered why people don't have an air pump connected to the in-tank diffuser (y adaptor and check valves), and timers so that when co2 is going through it, o2 isn't, and then o2 comes on when co2 ends, no additional equipment in tank... wouldn't this do the same as running an ir stone? all be it slightly finer?


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## dw1305 (12 Feb 2021)

Hi all,


john dory said:


> I was thinking more about what happens in the natural habitat.
> Wonder what the co2 profile would be any plant....let's say blyxa...where it occurs naturally.


It would depend a little bit on which <"photosynthetic pathway"> _Blyxa_ spp. have, but I'm going to assume that they are "C3" plants.  You also need to be aware of the <"BOD  concept">, because what happens is going to be dependent upon the microbial bioload as well as the density of plants (and fauna).

When light levels <"fall below LCP"> the plant becomes a net CO2 exporter, the <"stomata are shut"> and the oxygen in the <"lacunae and aerenchyma"> will be replaced by CO2 during respiration. Some CO2 will also diffuse into the water, and the plants will take some dissolved oxygen from the water.

You could measure these changes with a dissolved oxygen meter, but you could also look at pH. If you <"use changes in pH as a proxy for changes in CO2"> level (and the DO : CO2 ratio) you would need to know the carbonate hardness (dKH) of the water.

Once light levels exceed LCP the process is reversed, the stomata open and the internal CO2 is used in photosynthesis. The excess of oxygen replaces CO2 and, if the plant tissues and the surrounding water become saturated with oxygen, pearling occurs.

cheers Darrel


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## Wookii (12 Feb 2021)

Sammy Islam said:


> I find that my tank degasses the CO2 i have injected in about 1.5 hours without having to angle my lily pipe upwards. I only angle the lily upwards before i go to bed.


That is surprising to read Sammy? I have found on my tanks the only way to fully degas the CO2 overnight was to run two air stones during the entire lights out period (even then it would take way more than 1.5 hours), which I don't do. Even vigorous surface agitation wasn't sufficient to degas it all.

Without the air stones my tanks never fully degas all the CO2, based on the tank water pH and comparing to a fully degassed tank water sample stored in a cup for 24 hours.


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## Wookii (12 Feb 2021)

Personally I think heavy surface agitation or air stones are a good idea on a newly set-up tank, where the plant mass is naturally lower, and the plant growth and photosynthesis isn't in full swing. But once a tank has a high plant mass and is heavily photosynthesising during the photo period I would be more inclined to agree with @Geoffrey Rea's post here:



Geoffrey Rea said:


> Have actually found a caveat to this @alto
> 
> Borrowed a dissolved o2 meter from a friend at uni and found that on a mature high tech setup I was running, the air stones running at night were bringing night time o2 levels below what was available if solely relying on what was produced through photosynthesis alone during the photoperiod. Pretty obvious because of the gassing off. The significance of running the agitation in periods of trouble is that it guarantees a lower limit and should satisfy o2 needs at night in the absence of a healthy system. If there is no problem, there’s no need to deplete those levels to atmospheric equilibrium. Makes raising lily pipes moot if things are running fine post the first month onwards on high tech.
> 
> ...



I believe the water column saturates with enough DO to provide plenty for night time purposes, making airstones etc redundant. The exclusions to that being low plant mass layouts, and non-CO2 injected tanks which may not achieve DO saturation.


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## Fred Dulley (12 Feb 2021)

Wookii said:


> Personally I think heavy surface agitation or air stones are a good idea on a newly set-up tank, where the plant mass is naturally lower, and the plant growth and photosynthesis isn't in full swing. But once a tank has a high plant mass and is heavily photosynthesising during the photo period I would be more inclined to agree with @Geoffrey Rea's post here:
> 
> 
> 
> I believe the water column saturates with enough DO to provide plenty for night time purposes, making airstones etc redundant. The exclusions to that being low plant mass layouts, and non-CO2 injected tanks which may not achieve DO saturation.


Totally agree. It's almost as though folks believe the oxygen produced during the photoperiod just ups and disappears as soon as the lights are off.


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## dw1305 (12 Feb 2021)

Hi all,


Fred Dulley said:


> It's almost as though folks believe the oxygen produced during the photoperiod just ups and disappears as soon as the lights are off.


Unfortunately that has been the problem on some of the other forums I've belonged to.

People have been unwilling to accept that plants are <"net oxygen producers"> and have used the fact that low oxygen events occur during the night as conclusive, and irrefutable, evidence that I'm wrong, and that "_the plants have killed their fish"._

At that point telling them that the fish would already have died without the plants, and that their fish have been on life support for some time, only leads to <"bloodshed and heartache">.

cheers Darrel


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## Sammy Islam (12 Feb 2021)

Wookii said:


> That is surprising to read Sammy? I have found on my tanks the only way to fully degas the CO2 overnight was to run two air stones during the entire lights out period (even then it would take way more than 1.5 hours), which I don't do. Even vigorous surface agitation wasn't sufficient to degas it all.
> 
> Without the air stones my tanks never fully degas all the CO2, based on the tank water pH and comparing to a fully degassed tank water sample stored in a cup for 24 hours.


It does sound surprising but i have taken PH readings a lot, especially in the first 6 months when worrying about everything 🤣.

I feel like i have decent surface agitation from my EA lily and i also have a tiny 500LPH powerhead in the opposite corner which provides a little more agitation. After my CO2 turns off, i leave the powerhead on for an extra hour to help degass the CO2, by the time it it turns off my PH is about 7.8, fully degassed 7.9, during photoperiod PH 7.1.


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## Geoffrey Rea (12 Feb 2021)

dw1305 said:


> conclusive, and irrefutable, evidence that I'm wrong, and that "_the plants have killed their fish"._








They’ll be coming for us next @dw1305 😳


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