CO2 stability, brush algae and EI water change

[Gilles]

So i have Akadama, on some spots i am getting brush algae. Water is injected through a spraybar and it seems that the brush algae is appearing only on the ends of the spray bar where water circulation is less then in the rest of the tank. So you'd think that it is the water circulation but i really can't add more co2 and/or another water circulation at that point. Plants are 'wavy' also in the spot where i get those small amounts of brush algae.

So this leads me to another question. I am currently injecting CO2 directly into my inlet with a wooden airstone. Not all co2 is being dissolved since i sometimes get burps. So this means that my CO2 is way to high or the bubbles are to big. I just received (from green leaf aquariums USA) two bazooka atomizers, which i intent to place on either end of the tank. From one co2 line i have a splitter, 2 needle valves and 2 bubble counters which should allow me to spread the pressure evenly. If this won't get me better co2 then i am totally lost.

Another thing i heard from ceg is that algae only happens when co2 is instable, which i currently have, since i have a co2 controller and not 24/7 co2. But here comes the last confusion i have. When doing a 50% waterchange, i currently have like 30 minutes of instable co2 before my PH is reached and my drop checker is green again. This causes irradic behavior on my catfish. But if you have like 2-3bps co2 won't it take like a whole day before co2 is stable again? Won't this cause algae??

 

[RossMartin]

I could be wrong but I don't think it is recommended to use a PH controller. Most people turn the CO2 on two hours before lights on and turn it off one hour before the lights go off.


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[RossMartin]

I would also try and get a PH profile so you can see what is going on. This helped me with my issues.


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[X3NiTH]

Water changes are best performed either before the injection period or after. I do my 50% weekly water change on a Saturday night after the solenoid shuts off, this leaves me with an hour before lights out so I can see what I'm doing in the tank, I never water change within an injection period unless it's an emergency.

I have found that pH controllers are best used as a fail safe to prevent gassing the fish. You need to find a way to allow you to have a continuous injection rate that gets you to your required pH drop before the lights come on and then remain at that pH throughout the photoperiod. The stop start of a controller has too wide a variance at around +/-0.1pH, absolutely fine if there are no inhabitants present as you can crank up the gas way beyond whatever fish could survive and for plants to notice a shortfall. If you inject on the lean side which we all tend to do then plants will definitely notice a 0.2 total pH variance when a controller controls the injection.

I control my injection (I'm still on a controller for use as a safety cutoff and for monitoring pH) through 24/7 aeration (adjustable), I also use a 20" reactor after my canister filter fed co2 by an inline diffuser from which I get 100% dissolution of co2 into the water. My co2 injection rate is set so that it reaches an equilibrium with my aeration output that gives me a 1.2pH drop by lights on and stays there, although it may climb back up a touch an half an hour or so after lights on due to the plants consuming the co2, however I never let it go beyond 0.05pH from where it should be, this is where aeration comes into play, I decrease it slightly so that less co2 is driven off making more available to the plants so that when the pH balances out again it reaches an equilibrium with whatever the plants are able to consume, whatever oxygenation shortfall is happening due to decreased aeration it is being more than made up for by oxygen production being more stably produced by the plants, this is evidenced by all plants pearling by mid afternoon. If for any reason I see the fish heading towards the surface because something happened within the tank to allow more co2 to creep into it (? Photosynthesis slowing due to a nutrient shortfall) then I can increase the aeration (which is set initially to midway output) to drive out more co2 and increase oxygenation (the bubbles increase the surface area that the tank water can come into contact with air way beyond what my surface area can achieve).

Finding a way to get off the controller controlling the gas input also has the benefit that pH shifts by biological influences doesn't mess with how much gas goes into the tank, having the fish spoil the plants day by all going at once and dropping the pH enough to trigger the controller to shut off the solenoid is best avoided. The time spent throughout the week of adjusting the controller to combat the daily biological influences to the pH in an effort to keep the drop checker in the green, feels like it all goes to waste the next injection period after a water change when you find the fish at the surface being gassed because the water you changed with had a higher pH and the controller didn't get the memo!

Controllers are brilliant for monitoring the pH profile and a good safety net for the times when things go bad and the plants don't eat as much co2 as you're expecting them to thus hopefully saving the inhabitants from an untimely demise.

 

[Gilles]

I could be wrong but I don't think it is recommended to use a PH controller.

Yes i know but i first have to get my co2 injection in order before i try to switch to this kind of co2 distribution.

I would also try and get a PH profile so you can see what is going on.

Also true

I do my 50% weekly water change on a Saturday night after the solenoid shuts off, this leaves me with an hour before lights out so I can see what I'm doing in the tank, I never water change within an injection period unless it's an emergency.

This was the answer i was looking for, since doing it midday causes co2 instabillity! How long before lights go off do you stop co2?

The stop start of a controller has too wide a variance at around +/-0.1pH

Which i now have...

I control my injection (I'm still on a controller for use as a safety cutoff and for monitoring pH) through 24/7 aeration (adjustable), I also use a 20" reactor after my canister filter fed co2 by an inline diffuser from which I get 100% dissolution of co2 into the water.

So if i get this correctly you have co2 injection controlled by a timer and solenoid at some rate, which activates your inline diffusor. Then in another circuit you have an air pump which turns on if your PH gets to low?
Does the co2 then shut off, or does it keep flowing?

 

[Edvet]

Giles, if you do the waterchange before lights on and get the leaves out of the water they will take up a lot of CO2 (rub them clean too, it will help)
CO2 doesn't kill, to little O2 kills, so if you have plenty surface agitation it should be safe. Just keep it steady. (have a value the pH controler doesn't come on except in extreme values) For me it looks like you could have a circulation problem too. And using the wooden diffusor is not helping i guess. (building your own DIY diffusor outsside the tank on a separate pump is the best i think)
Having CO2 (solenoid) and surface agittion (24/7) on gives the mst stable situation, it will cost some extra CO2 but is the best and safest way i feel.

 

[eduard]

Hello Edvet,that is not true I am afraid.
in aquarium too much of Co2 kills.

 

[Gilles]

I think Edvet was referring to plants in relation with a waterchange

@Edvet i removed the wooden airstone this morning and replaced it with a GLA bazooka.

 

[X3NiTH]

No Edvet is right about co2 not being the killer, which is why I also mentioned oxygenation shortfall. You can put as much co2 as you like into the water as long as there is enough oxygen to support it. My surface area alone (without a spraybar as I'm using a crook) is too small at 12" square to deliver enough oxygen into the water hence the Airstone working for me, with a spraybar if done right you get peaks and troughs with the ripples and this increases surface area.

My co2 solenoid is plugged into a mechanical timer which is then plugged into the controller power port, it will go out of time synch if the controller shuts off the solenoid (if I'm out when an over gassing event happens I will know it's happened by the timer lagging behind current time).

My Airstone is a sintered glass type, I did have a wood type but I got rid of it because they block up and slow output (wood has finer bubbles and is more efficient than sintered glass but neither get anywhere near the efficiency that a bazooka attached to an airbrush compressor can deliver (doesn't fit in my cupboard)), it's not on a timer or controller, although having said this I am testing a controller that has the ability to work in the reverse direction of a co2 one (UP) so that it can be used to dose kalkwasser into a salty setup, I'm about to test controlled air injection using a secondary air pump to see if it can do the fine tuning without me having to get involved for a more hands free approach.

As Edvet said having an external reactor to put the co2 into the water is the best option, get it into the water before it goes into the tank. If you read TheBarrReport this appears to be the most efficient way to inject, although combined with a bean animal overflow and a wet dry sump system (TomBarr/Plantbrain uses this filtration and gets oxygen saturation 10% above ambient), this way you never have to worry that your atomiser is in the right place to work with the flow you have, it doesn't necessarily have to be on its own line as I run mine inline with my canister filter, but the consensus is on its own line is best.

 

[dw1305]

Hi all,

You can put as much co2 as you like into the water as long as there is enough oxygen to support it.

This is true for plants, but it isn't entirely true for animals. As CO2 users have found fish can acclimate to higher CO2, often by increasing their blood haemoglobin levels (which is why it takes a while).

The problem is that the haemoglobin carries both O2 and CO2, and it is the gradient between the CO2 levels in the blood (in the gills) and the water allows the CO2 to diffuse out and be replaced by O2. It doesn't matter how much oxygen you have, at some point the CO2 diffusion gradient will become too shallow and the fish will asphyxiate.

But what sort of fish you have, and how big they are, is also relevant. Big fish (volume increases as a cube, whilst gill area increase is nearer to a square) from cool, flowing water (cool water holds more oxygen, flowing water has a larger gas exchange area) are particularly at risk.

There are sub-lethal effects to long term high CO2 exposure, a lot of the work has been on Salmonids because they combine little tolerance to low oxygen levels with high commercial value. This is <"Effects of environmental hypercapnia on hemato-immunological parameters, carbonic anhydrase, and Na+, K+-ATPase enzyme activities in rainbow trout (Oncorhynchus mykiss) tissues">

There is a description here of the Bohr and Root effects here: <"Fish Respiration">.

cheers Darrel

 

[eduard]

http://www.ukaps.org/forum/threads/why-do-we-aim-for-30-ppm-co2.32428/page-3
The toxicity of CO2 has to do with the dissolved gas pressure in the water which makes it difficult for the fish to exhale. Imagine if I put a plastic bag over your head and forced you to re-breathe the air you exhale. Any living thing that consumes carbohydrates, and which burn the carbohydrates with Oxygen will always produce CO2 which has to be eliminated from their system. Within the bloodstream, the Carbonic acid that results from the tissue produced CO2 changes the pH of the blood and that acidity inhibits the Oxygen carrying ability of red blood cells. We and fish have to expel the CO2 or suffer hypoxia. High CO2 pressure in the water column pushes back against the fishes attempt to push CO2 out through the gills

 

[X3NiTH]

Sorry, I should not have been so general with that comment I should have added 'within reasonable limits' (even more precisely within the planted tank mantra of +30ppm (30ppm green DC, +30ppm green/yellow DC, ++30ppm yellow DC)). What I was really trying to say is that you can be in a situation when injecting co2 where you can't get the optimum pH drop to turn the drop checker green for the plants without the fish gasping at the surface, there is an equilibrium imbalance and the cause of it is the lack of oxygen to support the co2 going in. For any beginner this situation can be a real head scratcher and you begin to doubt if your Drop Checker is working correctly or that your pH meter is faulty, but the end result is the same the gas gets dialled back down and the plants suffer. The solution to that problem is to get more oxygen in the tank any way possible.

 

[ceg4048]

The level of CO2 in the water has nothing to do with the level of Oxygen that can be in the water.
CO2 is highly toxic because it acidifies the blood and prevents hemoglobin from holding onto Oxygen.
It won't matter how much Oxygen is dissolved in the water if there is too much CO2 because the fish will not be able to use it.
You cannot fix hypercapnia by adding more Oxygen, and you can't really add more Oxygen anyway because Oxygen has very poor solubility.
So people really need to forget about O2/CO2 equilibrium because that is pure fantasy.

Cheers,

 

[Edvet]

I agree CO2 can be toxic, but how often do you see to much CO2 when there is a lot of surface agitation? And isn't to little CO2 the most seen mistake in high light tank, coupled with faulty distribution. In a small tank there might be a bigger risk of CO2 overdosis, but in a larger tank i have yet to see it..
Again i agree CO2 and O2 dont exclude each other in solvability, but doesn't surface agitation drive out CO2 and increasse O2 uptake?

 

[X3NiTH]

Thanks Clive, can you explain by which mechanism fish are able to tolerate a higher level of co2 when you increase the surface area the water can contact the air by aeration or surface rippling. Is it more about persistence of co2 than available oxygen level?

 

[ceg4048]

Gases diffuse from one medium to another, or from one area to another strictly by virtue of the differences in the pressures of that gas between the media or areas.
When you inject CO2, the pressure of CO2 in the water increases and so it's at a higher pressure than the pressure of CO2 in the atmosphere just above the surface of the water.

This is exactly the same if I inflate a balloon. The air pressure in the balloon is higher than the air pressure surrounding the balloon.
If I open the stem of the balloon then the higher gas pressure escapes from the high pressure area inside the balloon to the low pressure area outside the balloon through the stem.

The diameter of the stem, and therefore the surface area of the hole in the stem, determines how fast the air can leak out.
If the stem diameter is larger, then the balloon will deflate faster. If I puncture the balloon, the fabric rips and opens a very large surface area, so the air escapes explosively fast.

When you agitate the surface of the water in the tank, either with bubbles, or by placement of the filter outlet, you are increasing the surface area of the waterline, so the CO2, as well as every other gas presently dissolved in the water escapes into the atmosphere IF the gas is at a higher pressure in the water than it is in the atmosphere. If any gas pressure is at a lower pressure than atmosphere, then this added surface area allows a faster influx of the gas from atmosphere into the water.

Adding CO2 to a tank increase the Oxygen production of plants and this Oxygen then dissolves in the water, which increases the pressure of Oxygen in the water. So, both CO2 and Oxygen are at a higher pressure in the water than they are in the atmosphere. Agitation of the surface allows faster escape of CO2 AND O2 from the water. So people are under the illusion that they are giving their fish more Oxygen by using bubbles or by agitating the surface, when actually they are giving the fish LESS Oxygen. But again, this doesn't really matter because it's the level of CO2 that has, by far, the higher toxic impact. CO2 has a much, much higher water solubility than Oxygen.

The surface agitation, in terms of Oxygen delivery, is much more important at night, when the CO2 is turned off, because the plants are still consuming Oxygen (but not producing Oxygen) and therefore they are competing with fish and bacteria for available Oxygen. This can lower the total Oxygen pressure in the water and so the situation is reversed at night. The surface agitation does the same job of increasing the surface area for gas transport, but this time the Oxygen pressure in the atmosphere can be higher than it is in the water, so Oxygen moves more quickly from atmosphere to water.

So actually, when you have a high surface agitation , it isn't at all the case that the fish are more adapted to a higher CO2 level. It's that the surface agitation is evacuating the CO2 from the water and so the level of CO2 in the water is reduced by the agitation.

Cheers,

 

[X3NiTH]

Thanks Clive, that was very informative.

 

[ian_m]

There were some experiments done with radioactive labelled oxygen via air pump into tank and via surface agitation into tank to see how O2 entered the water. It was found more O2 enters the water column via surface agitation than via an air pump contrary to what people had assumed. Also the air pump helped by creating further surface agitation and circulation currents further enhancing O2 take up via the surface.

Forgot add, one of the reasons for air bubbles not enhancing O2 is because in the tank they are at tank pressure and there is no or little pressure difference for O2 to diffuse in or out the tank.

 

[Joost]

Great post ceg! That was really interesting to read.