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Evaporation and the pH profile (ie. CO2 levels)

JoshP12

JoshP12

Member
Joined
8 Dec 2019
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Location
Canada
Hi everyone,

I have an ATO (auto top off) - but until then, I am curious.

I have recently lost lots of shrimps and noticed recursive behavior in my livestock after water changes. I want to be able to leave for 3 days without worrying about the tank (I have an auto doser) but this water evaporation is killing me.

After water change day (yesterday), today I noticed signs of CO2 suffocation in an Amano shrimp (unfortunately, I know the signs now :arghh:) --yesterday was the absolute healthiest I have seen all of my tank mates, absolutely no lethargy in animals and plants very healthy. I will set my ATO at that height. But for now, I noticed that about 1/2 inch to an inch of water (impacting surface agitation of course) is literally throwing my CO2 levels (or my O2: CO2 ratio) off - so I am walking a fine line.

I find it crazy the impact surface agitation has; prior to this, I removed my skimmer (just to see) and killed more shrimp :arghh: because of surface scum build up :banghead: ... so gaseous exchange is real.

I could turn down CO2, but it is stable and clearly (since I observed yesterday) is at a great level.

Misery loves company - has anyone else observed this or have any insights to share?

I am in pursuit of finding the level that I can top it off to, without killing livestock and be able to not drop my CO2 so far down from evaporation (which I also noticed on day 3 of a different top-up level my DC was way greener than usual 😵).

How often do you guys do it? Do you do it daily?

Josh

Oh, I should add my neons show no signs of distress - the only ones that do are the Amanos and then my otto cat's sometimes go closer to the top (which I know now is a sign -- they hover differently).

EDIT: Or does this just not matter and I should just top it off lower and not worry?
 
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Hi @JoshP12
JoshP12 said:
... so gaseous exchange is real.
Click to expand...

It most certainly is. I wonder how many people do a pH profile and then set CO2 injection rate/timing + lights timing to suit, then find that even the thinnest layer of scum can cause CO2 concentration to rise beyond the 30 ppm 'safe limit'? If a surface skimmer gets bunged up, this may be all that it takes.

So, here's a thought - could you use your pH probe/monitor to control the ATO in some way? Or, is it a DO probe that you have?

JPC
 
I've also noticed this.

I had to do my PH Profile much closer to the minimum water level (water level on the sixth day after water change), and learn not to fill the tank too high.

If I go too high I get less agitation and higher CO2 build up. I now fill to about an inch below the rim, I then get a further inch / inch and a half drop over the week, but this doesn't throw my C02 off too much.

Essentially I have greater agitation all week, which means higher evaporation, but low contrast between agitation from day one to seven - and I've tuned CO2 for this higher agitation.

I don't top up during the week, but I guess tank size and the volume to surface area ratio will make this very individual for each tank.
 
jaypeecee said:
Hi @JoshP12


It most certainly is. I wonder how many people do a pH profile and then set CO2 injection rate/timing + lights timing to suit, then find that even the thinnest layer of scum can cause CO2 concentration to rise beyond the 30 ppm 'safe limit'? If a surface skimmer gets bunged up, this may be all that it takes.

So, here's a thought - could you use your pH probe/monitor to control the ATO in some way? Or, is it a DO probe that you have?

JPC
Click to expand...

Thanks JPC! I am running a 4 day pH probe test to see if with evaporation the pH minimum actually increases. I would just set the ATO to the level that I know works well with my pH drop and that will stay consistent ... rule out more and more factors.

I can attest to exactly that. I saw 2 Amano perish + neons gasp + otto faint one day and the only difference was the build up of surface scum -- I saved the neons and the otto. This tells me that my CO2 is at this range of dicing with death. 1 day everyone is good, the next day that happens. The only difference was scum + CO2.

The thing that I hate about this hobby is that our mistakes cause death; it's not like cooking where I can eat my burnt food.

Josh
 
Nick72 said:
I've also noticed this.

I had to do my PH Profile much closer to the minimum water level (water level on the sixth day after water change), and learn not to fill the tank too high.

If I go too high I get less agitation and higher CO2 build up. I now fill to about an inch below the rim, I then get a further inch / inch and a half drop over the week, but this doesn't throw my C02 off too much.

Essentially I have greater agitation all week, which means higher evaporation, but low contrast between agitation from day one to seven - and I've tuned CO2 for this higher agitation.

I don't top up during the week, but I guess tank size and the volume to surface area ratio will make this very individual for each tank.
Click to expand...

It makes me feel better to know that someone else has noticed and seen this.

Thanks for sharing.

EDIT: Have you noticed any adverse affects throughout the week by having decreasing CO2 levels each day? @Nick72
 
JoshP12 said:
The thing that is crazy for me (throughout this learning curve) is that my neons were unaffected, my ottos were mid range, and my amanos died.
Click to expand...

Hi @JoshP12

I did some digging to see if there were any scientifically-derived upper limits for CO2 toxicity on shrimp and found this:

"The highest concentration that did not induce significantly higher mortality was 23.8 mg/L of CO2".

You can read more here:

https://aquariumbreeder.com/co2-in-a-shrimp-tank/

Michael, the author of this article is very helpful. I was in touch with him a few weeks ago. You can contact him directly from the above website.

JPC
 
Nick72 said:
...I guess tank size and the volume to surface area ratio will make this very individual for each tank.
Click to expand...
Hi @Nick72

Yes, I agree. And, in order to get optimum exchange of gases, it's the surface area to volume ratio that needs to be maximized, isn't it? Or, is it? On the one hand, we want to retain CO2 but we also want to maximize oxygenation of the tank water. Wouldn't it be better if we didn't need to rely on CO2 in the first place? It may be the best source of carbon for the plants but it's a tricky one to control and optimize. Yes/No?

JPC
 
jaypeecee said:
Hi @JoshP12

I did some digging to see if there were any scientifically-derived upper limits for CO2 toxicity on shrimp and found this:

"The highest concentration that did not induce significantly higher mortality was 23.8 mg/L of CO2".

You can read more here:

https://aquariumbreeder.com/co2-in-a-shrimp-tank/

Michael, the author of this article is very helpful. I was in touch with him a few weeks ago. You can contact him directly from the above website.

JPC
Click to expand...

Thanks! That is great! I will read through to see how Amano's fair in here.

Josh
 
jaypeecee said:
And, in order to get optimum exchange of gases, it's the surface area to volume ratio that needs to be maximized, isn't it?
Click to expand...
It's back to basics isn't it?
Old-time aquarists didn't know their phosphate levels, Ca/Mg ratios or PAR. But they knew gas exchange was important, and that surface area was important for good gas exchange. It seems to have got forgotten somewhere.
 
Hi @JoshP12

On the basis that "The highest concentration that did not induce significantly higher mortality was 23.8 mg/L of CO2", how does your tank stack up against this figure?

JPC
 
jaypeecee said:
Hi @JoshP12

On the basis that "The highest concentration that did not induce significantly higher mortality was 23.8 mg/L of CO2", how does your tank stack up against this figure?

JPC
Click to expand...

I am not sure; clearly, I was over that amount today. A pH drop of 1.2/3ish maybe and a lime green DC; more importantly,there has been no new algae on new growth - old algae is still growing but slow and I will just trim it away as more leaves come in - and plants are healthy, so the only tell tale is the distress on the Otto cats - so whatever their max threshold is maybe knock a couple off that and that was my level.

In terms of moving forward, I decided just to top it off as @Nick72 is doing - at that level just high enough and top it off every couple days and move on to more important things to fix in the tank. When I am way, I will just have someone fill it up to the line that I leave - until the Auto Top Off gets here.

I think for the sake of this, I learned a lot and realized how much thought goes into dialing in CO2 - and how toxic the substance really is.

Josh
 
sparkyweasel said:
It's back to basics isn't it?
Old-time aquarists didn't know their phosphate levels, Ca/Mg ratios or PAR. But they knew gas exchange was important, and that surface area was important for good gas exchange. It seems to have got forgotten somewhere.
Click to expand...

A lot of basics aren't discussed.

I am relatively new to the hobby and simple things like making sure my water change water was the same as my tank water was never "taught" to me. Sure, it would've been easy if I just used tap water, did my water change regularly, did maintenance properly (which I had no clue how to do), and moved on. But the advice that I received from LFS and the hodge-podge of reading that I did didn't help (well it did, but ... I think you know what I mean).

For this reason, I am thankful for finding UKAPS; with a math/science background, I can't just follow what people "say", I truly need to understand what is happening.

I am sure it would be much easier if I just followed a design that said, buy this tank, use that output, put that output there, put that skimmer on the input, buy all your plants at tropica in those little cups, buy a doser, buy an ATO, etc etc -- but I am part thrifty too 😉 ... and I suppose the emotional rollercoaster of this hobby keeps me in it HA.
 
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JoshP12 said:
I am sure it would be much easier if I just followed a design that said, buy this tank, use that output, put that output there, put that skimmer on the input, buy all your plants at tropica in those little cups, buy a doser, buy an ATO, etc
Click to expand...
That's only easier until it goes wrong. 🙂
If you know why you are doing things you are in a better position to work out the cause of any problems.
 
Hi all,
JoshP12 said:
For this reason, I am thankful for finding UKAPS; with a math/science background, I can't just follow what people "say", I truly need to understand what is happening.
Click to expand...
Yes I'd agree, it absolutely amazes me that people are willing, for example, to use CO2 without fully understanding the dangers and/or the chemistry involved.

However knowledgeable, and skillful, you are sooner or later this hobby will always <"bite you in the bottom">, all you can do is try and prolong the time interval to "later".

cheers Darrel
 
dw1305 said:
Hi all, Yes I'd agree, it absolutely amazes me that people are willing, for example, to use CO2 without fully understanding the dangers and/or the chemistry involved.

However knowledgeable, and skillful, you are sooner or later this hobby will always <"bite you in the bottom">, all you can do is try and prolong the time interval to "later".

cheers Darrel
Click to expand...

It's hard - several months ago I had only awed at the CO2 enriched aquariums - and all you think (when you don't know any better and are new into the hobby) is lets do it. Several hundred dollars later, you realize that learning CO2 is harder than keeping fish itself.

The guilt of deaths is rarely discussed.

For every 100 posts on nutrients, there is 1 person who admits to gassing fish (I made this figure up). I love the idea of the pH profile as it gives some structure to learning; conversely, the notion of mastery and watching your fish requires expertise that inevitably only comes from gassing/nearly gassing everything. 🧐


Josh
 
JoshP12 said:
It's hard - several months ago I had only awed at the CO2 enriched aquariums - and all you think (when you don't know any better and are new into the hobby) is lets do it. Several hundred dollars later, you realize that learning CO2 is harder than keeping fish itself.
Click to expand...

Hi @JoshP12

I'm so full of thoughts but don't know where to begin. But, I'll make a start and hope it makes sense! If not, I'll try again.

Perhaps one of the difficulties in keeping healthy plants arises because we try to use water that is low in bicarbonates ('low' KH). As Diana Walstad* points out:

"...plants that can use bicarbonates (in addition to CO2) have an enormous advantage in alkaline water".

Apparently, half of the aquatic plants tested** (almost thirty years ago) can use bicarbonates.

I translate that to mean I may be better off using plants whose natural habitat is hard water. And I've been keeping mine in soft water. 😱

Food for thought?

JPC

* Ecology of the Planted Aquarium

** Madsen TV and Sand-Jensen K. 1991 Photosynthetic carbon assimilation in aquatic macrophytes. Aquat. Bot. 41: 5 - 40
 
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