Floaters and CO2

[Majsa]

How do you manage your surface agitation and gas exchange with a lot of floaters in the tank?

I started a 54L (60cm) tank 5 weeks ago and I am trying to get the CO2 right. I recently added a new portion of Salvinia to the tank and changed the green Eheim wide jet outflow pipe (which was capable of messing the floaters and even the substrate) to a stainless Chihiros inflow & outflow set. The filter is Eheim eXperience 150 (500l/h), substrate is Tropica Soil Powder.

How important is degassing CO2 during the night? My drop checker stays apple to lime green all day and night, while I run CO2 7 hours a day (2 hours before lights on and 2 hours before lights off). The PH is around 6.4 during the day and 6.6 in the morning. I run an air stone tonight but that wasn't a success, my son woke up much too early to the noise and it didn't make much difference either. I took some tank water in a glass this morning and just measured the PH, it had risen to 7.1. Is this where I should be aiming for just before the CO2 goes on, or does it not matter? I want to make this a good home for the CPDs and shrimp when they move in after the holidays (the tank is temporarily housing two amano's and they are not bothered about anything).

This morning I lifted the outflow to the highest where I think it can be without pushing the floaters under water, let's see how that goes. The end of the outflow is detachable so maybe fitting in a custom glass lily pipe would work, do you think? Or one of those stainless pipes with a flat end? I don't trust myself with full glass pipes. I gave two handfuls of Salvinia to a friend yesterday and put one handful in another tank, but see hardly any difference, it must be growing like mad!

 

[Zeus.]

How important is degassing CO2 during the night?

As long as the pH is increasing once lights are off even if it doesnt flat line before the CO2 comes on I cant see it making any difference as long as theres enough O2 for the livestock and plants. If the livestock is at the top of the tank in the morning or before CO2 on gasping they may be in the areas of higher [O2] as fish do have O2 receptors in there gills. If there are happy at all depths cant see it being an issue.

Impressive floating carpet

 

[Majsa]

Thanks Zeus! Does this mean the levels of O2 are independent from CO2, so even if the drop checker stays green all the time, it doesn't necessarily mean there is less / too little oxygen in the water during the night? So you would only know more about the O2 levels by watching the fish or actually measuring the O2. And the 1 point PH drop is not carved in stone, but just a guideline. Could it be that the floaters are slowing down the PH increase by releasing a lot of CO2 at night?

 

[Zeus.]

Does this mean the levels of O2 are independent from CO2

Yes

so even if the drop checker stays green all the time, it doesn't necessarily mean there is less / too little oxygen in the water during the night?

Correct , you can have high [CO2] and high [O2] like when lights have been on a few hours pearling starts when the water is saturated with O2 but CO2 is still high.

So you would only know more about the O2 levels by watching the fish or actually measuring the O2

Yep, if fish not in distress whats the issue, if you add more livestock you would need to be careful as they will need to acclimatise, plus the extra load may just tip the balance and there not be enough O2 plus CO2 output would increase also by the extra livestock plus their excrement would also increase O2 used in the biological break-end too IMO, But with your air stone running at night you should be fine IMO

And the 1 point PH drop is not carved in stone, but just a guideline

Yes a safe place for livestock and helps provide enough carbon for the plants to bombard with a higher rate of photos and they are able to handle the photos without melting/holes

Could it be that the floaters are slowing down the PH increase by releasing a lot of CO2 at night?

yes massively IMO, after all that fantastic floating carpet of yours cuts the surface area of the tank by a good 90% at least. if i leave the glass lids of mine they degas quicker.

My DC doesnt always turn blue before CO2 on with glass lids , also some of my plumbing on my independent line which I use to boost turnover in the tank got noisy with trapped air in pipes, so I had it going off from 11pm till 7am for a few days, the DC and pH wasnt giving the normal change then, Cleaned the pipes out increased the flow in pipes no air trapped nice and quiet so have it back on again all night, pH and DC changing normal again

Was doing a pH profile on my tank today and airstone was on all night and the pH didnt reach its peak pH until 1hr before CO2 on. DC was blue but I do have the bubbles from the airstone bubbling in to it at night so that colour change isnt the water [CO2]

 

[Majsa]

Thanks, I am starting to get it

But with your air stone running at night you should be fine IMO

I am afraid I had to take off the air stone, the tank is in my son's room and can't risk his good night sleep...Any noiseless options?

The plants are pearling during CO2 on, so there is a lot of O2 in during the day, hopefully a good reserve for the night too. I will keep on observing the tank, see what happens with less floaters, take a PH profile...Livestock can be added gradually when I think the tank is ready.

 

[Edvet]

Can you run it on a timer just as the light goes out for an hour? This will drive a lot of CO2 out already.

 

[Majsa]

Can you run it on a timer just as the light goes out for an hour? This will drive a lot of CO2 out already.

A good idea, I could even shift the photo period with an hour or so to get more time for the air stone. Does it make sense to run it again in the morning before the CO2 goes on?

 

[Edvet]

Don't think so, run it to remove the initial surplus.

 

[tiger15]

Don't think so, run it to remove the initial surplus.

Yes, running the air stone can drive off the surplus O2.

If the surface is completely covered by floating plants, it can cut off air exchange, but not transpiration exchange during photo period, and respiration exchange off photo period. l have a planted shrimp bowl (avatar) that receives 4 hour direct sun light. At the peak of sunlight, I notice strong pearling in the floater roots, raising pH from 7.2 to 8.5 by stripping CO2 to near zero and super saturating the water with O2. At night, the reverse is happening: CO2 up, O2 down, and pH down. The balance depends on the fish load and plant mass. Aeration at night may do more harm than good by driving off O2 and CO2 fish and plants need. Ultimately, if fish aren't grasping for air in the morning, it must be OK.

 

[Edvet]

Aeration at night may do more harm than good by driving off O2 and CO2 fish and plants need.

Don't think so. At night the plants are producing CO2 and using O2. CO2 can be blown out by airation easily, while O2 is much more "bound" to the water and more easily added through some surface movement.

 

[tiger15]

Don't think so. At night the plants are producing CO2 and using O2. CO2 can be blown out by airation easily, while O2 is much more "bound" to the water and more easily added through some surface movement.

I think CO2 is more bound to water than O2. CO2 has higher solubility than O2, and can coexist in free CO2 and ionized CO3 , whereas O2 exists in free O2 form only.

The OP does not run CO2 at night, so driving off excess CO2 at night to prevent poisoning is unnecessary. The water is likely super saturated with O2 after day time photosynthesis due to floaters blocking air exchange. At night, both plants and fish breath, and the level of CO2 and O2 will rise and fall, respectively. There could be surplus O2 to last all night long, and running the air stone will drive off that surplus. Additionally, aeration will drive off CO2 piled up at night that plants can utilize when photo period returns. The gas balance dynamic is complicated by the presence of floaters as well as dependent on other factors such as plant mass, plant health and stocking. If the fish aren't gasping for air in the morning, I would say there is no benefit to run air stone at night.

 

[Edvet]

I think CO2 is more bound to water than O2

It may look that way under pressure but in our tanks we loose CO2 with the slightest movement from the water, be it falling some distance to a sump or surface movement, the water looses the CO2 quite fast. That's why we need all the effort to get it in the collumn: diffusors, reactors getting it in a filtercannister. I don't know the excact fysical laws for this, but i know we loose CO2 in a heartbeat while adding O2 is as simple as adding surfacemovemnent.
Clive can probably explain this scientifically.

 

[tiger15]

In CO2 injected water, CO2 is dissipating faster than O2 with moving water due to steep gradient of CO2 concentration in the water towards the atmosphere. O2 concentration gradient is milder at best during photo period or in the opposite direction. At night, water movement can help replenish O2 if it is depleted by respiration. With floaters blocking physical gas exchange, the dynamic is different. O2 can be super saturated by pearling during the day, which may have enough surplus to sustain respiration during night if it is not driven away by air stone.

 

[Zeus.]

Plus Air [O2] 20%, [CO2] 0.04% so [O2] in air is x500 that of [CO2]

 

[Majsa]

A bit confusing, never heard of air stones driving off O2. I have a JBL O2 test, but have no clue if that's reliable. I took a reading yesterday morning and it was approximately 6 mg/l. Also run an air stone for one hour rather vigorously yesterday evening, and in the morning the PH was 0,1 higher than the previous morning. The DC still light green.
I am not drawing any conclusions yet, haven't had the time to take proper measurements yet (at set times, with/without air stone, need to recalibrate again etc.). Looking at the Amanos I don't think we're in big trouble here (and the DC was really bright lime / yellowish green when I came from work today), but I do want to have the CO2 sorted out before moving in more livestock.

About floating plants, if they have unlimited access to CO2 in the air, will they then also benefit from the O2 in the air at night, meaning they wouldn't push that much CO2 in the water after all, but just block the release of CO2 from the tank (produced by diffusion at daytime, fish and plants at night)?

 

[tiger15]

A bit confusing, never heard of air stones driving off O2. I have a JBL O2 test, but have no clue if that's reliable. I took a reading yesterday morning and it was approximately 6 mg/l. Also run an air stone for one hour rather vigorously yesterday evening, and in the morning the PH was 0,1 higher than the previous morning. The DC still light green.
I am not drawing any conclusions yet, haven't had the time to take proper measurements yet (at set times, with/without air stone, need to recalibrate again etc.). Looking at the Amanos I don't think we're in big trouble here (and the DC was really bright lime / yellowish green when I came from work today), but I do want to have the CO2 sorted out before moving in more livestock.

About floating plants, if they have unlimited access to CO2 in the air, will they then also benefit from the O2 in the air at night, meaning they wouldn't push that much CO2 in the water after all, but just block the release of CO2 from the tank (produced by diffusion at daytime, fish and plants at night)?

6 mg/l in the morning is kind of low, as standard for healthy stream is 5 mg/l O2 minimum. The reading looks suspect, but not impossible as morning O2 is supposed to be the lowest due to respiration and lack of photosynthesis all night long. I would measure O2 at the end of the photo period, and again after aerating the water for an hour to see the difference. Your O2 meter readings may not be accurate, but it may be good enough for comparison purposes.

Normally aeration should increase O2 and decrease CO2. But if the water is saturated with O2 from photosynthesis, the reverse can occur. Gases move in the direction of lower concentration. . Were your plants pearling at the end of the photo period? If so, there is chance the water is saturated with O2. Pearling can only occur if the water is already saturated with O2 as it cannot dissolve any more O2

I have a shrimp bowl with no filtration, no aeration and heavily covered with floaters and carpet plants. It receives 4 hour window sunlight daily and by the middle of the photo period, the plants are covered with bubbles. The bubbles don't dissipate until late evening, apparently the water continue to be saturated with O2 for hours. If aeration is provided, O2 saturation will be dissipated quickly.

 

[Majsa]

Yes, the plants are pearling. It is a bit difficult to interpret the O2 test as you need to compare colours, but I'd say it was at least 6, maybe 7. I will take some more readings in the weekend and next week.

 

[AverageWhiteBloke]

My understanding is that increased o2 can result in increased co2 via filter production. I think I came across this when someone was explaining how increasing o2 can actually create more carbon through co2 than liquid carbon can produce carbon at standard dosing. That being the case increasing o2 but not disturbing the water surface by it being muffled by lots of floaters and not driving co2 off could increase co2 no?

 

[AverageWhiteBloke]

Not sure about the PH drop either, you would have thought that if there's 30ppm (for arguments sake) there when lights go on or 30ppm is there 24/7 it should make no difference as long as there's enough in the lighting period. The plants are just wanting co2 I don't think they are particularly looking for the "drop". I had green DC at all times when I suffered a bit from surface scum and the plants were fine. After installing a skimmer it would go blue by the morning but obviously I had to turn up the gas to compensate for the loss through a clearer surface. I don't think the co2 is the worry more the o2 over night but if the fish are fine I would say the plants are creating enough through the lighting. Floaters will also transport o2 down into the column through the roots.

 

[Majsa]

The plants are just wanting co2 I don't think they are particularly looking for the "drop".

There are people running CO2 24/7 with good results so that must be true.

I want to understand what's going on in my tank so I made a plan. It's obviously not going to be the final truth as things change (livestock, temperature will change etc.) but if it works, I will have some sort of a base line. And I am curious to see what the effect of the air stone will be.

I've increased the light period to 8 hours but kept the CO2 at 7 hours, the idea is that the plants will have more time to use up the CO2 at the end of the light period.
Also removed all the tiniest Salvinia and kept the bigger ones, so that even though the surface is still mostly covered, there is more space (water/air) between the leaves. Recalibrated the PH meter.

I am going to measure PH and O2 at 8 pm (lights out), one hour later as tiger15 suggested and once or twice in the morning. First a few times without the air stone and then with the air stone running from 8 to 9 pm.

Today (WC day) the measurements at 8 and 9 pm (no air stone) were the same, PH 6.4 and O2 8. Also learnt that at 25C water can hold approximately 8 mg/l, so the water was pretty much saturated with oxygen (plants pearling). Today's conclusions: 1) the O2 test is accurate enough if you can read it properly 2) there isn't much point measuring the O2 when the plants are pearling The DC looked like a little Granny Smith apple all day.