Which centrepiece/show fish for my planted community aquarium?

[dw1305]

Hi all,

Surely adding CO2 will decrease the PH

Yes you are right <"it does">. This is actually how a <"drop checker"> works.

I'm not a CO2 user because I don't want rapid plant growth and I favour a <"risk management approach"> to fish keeping. I see accidental asphyxiation as a risk factor when you add CO2, but I don't see the pH fall as a risk.

When you inject CO2 a very small proportion of that added CO2 goes into solution as carbonic acid (H2CO3), and that carbonic acid disassociates into a bicarbonate ion (HCO3-) and a hydrogen ion or proton (H+) (I'm going to ignore the hydronium ion for this reply). Acids are defined as <"proton donors"> so the pH falls.

If we have "carbonate buffering" (dKH) some of that goes into solution and two of the "spare" H+ joins with the carbonate ion CO3 (base or "proton acceptor") to form 2HCO3 and we go back to the <"pH equilibrium point">.

The pH equilibrium point for water, with some dKH, is ~pH 8, but this is dependent upon the level of dissolved CO2, and that level is dependent upon the level of CO2 in the atmosphere. When we add CO2 we mimic a more CO2 rich atmosphere and the pH falls.

So surely the alkalinity isn’t the thing affecting the fish it would be the direct addition of CO2 causing a more acidic environment?

I wouldn't ever add CO2 if I kept <"Lake Tanganyika cichlids">, but it doesn't appear to worry other fish. As an example to get to "30ppm CO2" Aquascapers aim for a fairly rapid fall of one pH unit for when the lights turn on and an even more rapid rise of one pH unit when the lights go off. I pH changes themselves were deadly they would kill their fish every day and they don't, in fact they have some of the healthiest fish you will ever see. These are @Iain Sutherland's Congo Tetra

The addition of CO2 does <"have effects on snails">. When the pH is below pH7 calcium carbonate (CaCO3) will go into solution and they begin to show shell erosion. This is the same mechanism that could lead to <"coral reef collapse"> if <"atmospheric CO2 levels keep on rising">.

cheers Darrel

 

[mort]

My LFS prices 3 of these rainbows at £25

I've not been to a lfs for a couple of years so don't know how much prices have jumped but that seems pretty extortionate considering they were 3 for a tenner or so when I did last go. Might have to get the breeding tank setup if they are now that much. They are nice fish though.

 

[Animallover]

Judging from your current stock, you have very active, constantly moving fish. You need a a slow moving, inactive center piece fish. Gourami and cichlid are relatively inactive fish, but keep a single male to avoid conspecific aggression resulting in chasing. Blue dwarf and pearl gourami are slow moving, and have small mouth that won't harm tetra. Blue rams are good too and you can keep a pair as they bond strongly.

Blue rams looks great! But I’ve read they can eat shrimp so I’d rather not take the risk plus looks like they need higher temps and softer water and look quite tricky to keep compared to other fish. I had blue dwarf gouramis they were great just looking to try something different. Pearl gouramis look great too so will look

Hi all,

Yes you are right <"it does">. This is actually how a <"drop checker"> works.

I'm not a CO2 user because I don't want rapid plant growth and I favour a <"risk management approach"> to fish keeping. I see accidental asphyxiation as a risk factor when you add CO2, but I don't see the pH fall as a risk.

When you inject CO2 a very small proportion of that added CO2 goes into solution as carbonic acid (H2CO3), and that carbonic acid disassociates into a bicarbonate ion (HCO3-) and a hydrogen ion or proton (H+) (I'm going to ignore the hydronium ion for this reply). Acids are defined as <"proton donors"> so the pH falls.

If we have "carbonate buffering" (dKH) some of that goes into solution and two of the "spare" H+ joins with the carbonate ion CO3 (base or "proton acceptor") to form 2HCO3 and we go back to the <"pH equilibrium point">.

The pH equilibrium point for water, with some dKH, is ~pH 8, but this is dependent upon the level of dissolved CO2, and that level is dependent upon the level of CO2 in the atmosphere. When we add CO2 we mimic a more CO2 rich atmosphere and the pH falls.

I wouldn't ever add CO2 if I kept <"Lake Tanganyika cichlids">, but it doesn't appear to worry other fish. As an example to get to "30ppm CO2" Aquascapers aim for a fairly rapid fall of one pH unit for when the lights turn on and an even more rapid rise of one pH unit when the lights go off. I pH changes themselves were deadly they would kill their fish every day and they don't, in fact they have some of the healthiest fish you will ever see. These are @Iain Sutherland's Congo Tetra

The addition of CO2 does <"have effects on snails">. When the pH is below pH7 calcium carbonate (CaCO3) will go into solution and they begin to show shell erosion. This is the same mechanism that could lead to <"coral reef collapse"> if <"atmospheric CO2 levels keep on rising">.

cheers Darrel

thanks darrel I could follow that just about but have nothing to add haha. Those Congo tetras look stunning

I've not been to a lfs for a couple of years so don't know how much prices have jumped but that seems pretty extortionate considering they were 3 for a tenner or so when I did last go. Might have to get the breeding tank setup if they are now that much. They are nice fish though.

yup haha quite expensive considering I’m still pretty new so might make mistakes. Sounds like a good side hustle the breeding

 

[tiger15]

All fish will eat shrimplets if they have a taste for brine shrimp and can spot them, including small tetra. If you have heavy vegetation for shrimpletss to hide, some will make it even in the presence of rams.

 

[dw1305]

Hi all,

thanks darrel I could follow that just about but have nothing to add

The problem is that pH is just a complicated subject area anyway, and when you add extra CO2 into the equation you've added another layer of complexity.

I should have said that the pH changes due to changing dissolved gas ratios are really common and occur every day when <"plants are photosynthesising">. The only difference between <"soft and hard vegetated water"> is that these cyclic <"diel pH variations"> are smaller in harder water.

This is an <"oxygen example">, where the extremely high levels of oxygen (a base) have elevated pH.

it was a pond and the water sample had a dissolved oxygen level of 180% (~20oC, 18mg/L DO) and a pH value of pH 10.5.

cheers Darrel

 

[tiger15]

Hi all,

The problem is that pH is just a complicated subject area anyway, and when you add extra CO2 into the equation you've added another layer of complexity.

I should have said that the pH changes due to changing dissolved gas ratios are really common and occur every day when <"plants are photosynthesising">. The only difference between <"soft and hard vegetated water"> is that these cyclic <"diel pH variations"> are smaller in harder water.

This is an <"oxygen example">, where the extremely high levels of oxygen (a base) have elevated pH.


cheers Darrel

It depends on the type of water bodies. In lakes with submerged vegetation, diurnal pH can fluctuate greatly. For example, Lake Okeechokee, an alkaline and eutrophic lake in Florida, has measured pH fluctuated between 7.5 to 9 daily. Many freshwaters, however, have no submerged plants, for example, Amazon black water streams have stable pH of around 4 as water is too opaque to have submerged plants and algae.

I don't think oxygenation raises pH, but rather the depletion of CO2 from photosynthesis does. In my window sill zero tech planted bowls, pH fluctuated between 7.4 to 8.5 in daily cycle.

 

[dw1305]

Hi all,

Amazon black water streams have stable pH of around 4

They have a low pH, from a combination of the total lack of carbonates (or any other ions) in the water and humic and tannic substances from fallen leaves and wood. If we measured the TDS it would be reasonably high, but the ionic component is negligible leading to conductivity values in the 10 - 20 microS range. As you say it is plants that make the difference.

I don't think oxygenation raises pH, but rather the depletion of CO2 from photosynthesis does. In my window sill zero tech planted bowls, pH fluctuated between 7.4 to 8.5 in daily cycle.

No, oxygenation definitely raises pH*. I think you are right that normally it is the ratio of CO2 : O2 that matters, but you can get situations where <"oxygen production raises the pH well above the pH 8"> carbonate ~ CO2 equilibrium point **.

won't tell you the location, or context, but it was a pond and the water sample had a dissolved oxygen level of 180% (~20oC, 18mg/L DO) and a pH value of pH 10.5.

Edit: It doesn't and I should have known that. * It isn't the oxygen, it is just the CO2 depletion (via photosynthesis) that raises the pH.

cheers Darrel

 

[tiger15]

No, oxygenation definitely raises pH. I think you are right that normally it is the ratio of CO2 : O2 that matters, but you can get situations where <"oxygen production raises the pH well above the pH 8"> carbonate ~ CO2 equilibrium point.

cheers Darrel

Darrel, I don’t understand the chemistry that would support pH increase from oxygenation alone.

If you let tank water sample sit overnight, pH will increase due to CO2 off gassing. If you aerate water with an airstone, pH will increase even faster by stripping off CO2. However, if you dose peroxide or inject O2 gently into water, it will have no effect on pH.

Photosynthesis will increase pH by carbonate acid removal (CO2 uptake) and to a lesser degree, nitric and phospheric acid removal (N and P uptake) but has nothing to do with oxygrpeation per se.

 

[dw1305]

Hi all,

Darrel, I don’t understand the chemistry that would support pH increase from oxygenation alone.

Oxygen is a Lewis base (that too a weak one)........

REASON: It has lone pair of electrons, which can be donated to electron-deficient species (Lewis acids).

Simple enough <"oxygen is a base">, if you super-saturate the water with oxygen the pH goes up*.

Photosynthesis will increase pH by carbonate acid removal (CO2 uptake) and to a lesser degree, nitric and phospheric acid removal (N and P uptake) but has nothing to do with oxygrpeation per se.

I'm not sure what you mean. All the oxygen we breathe is as a result of the excess oxygen that plants produce during photosynthesis. For every one molecule of carbon dioxide incorporated a molecule of oxygen is produced. Plants are carbon based and they grow, that growth is a measure of the excess oxygen production.

I had an interesting one today. I won't tell you the location, or context, but it was a pond and the water sample had a dissolved oxygen level of 180% (~20oC, 18mg/L DO) and a pH value of pH 10.5...............

Plants "pearl" this is when the level of dissolved oxygen in the water exceeds 100%.

When we sealed the water collection bottles (collected with a <"Phil sampler">) the green water algae were pearling very noticeably...........

Quotes from <"A question.......">.

Edit * It doesn't, this is only true when photosynthesis has stripped the CO2 from the water. It is a CO2 effect, not an oxygen one.

cheers Darrel

 

[tiger15]

Hi all,


Simple enough <"oxygen is a base">, if you super-saturate the water with oxygen the pH goes up.

I'm not sure what you mean. All the oxygen we breathe is as a result of the excess oxygen that plants produce during photosynthesis. For every one molecule of carbon dioxide incorporated a molecule of oxygen is produced. Plants are carbon based and they grow, that growth is a measure of the excess oxygen production.

Plants "pearl" this is when the level of dissolved oxygen in the water exceeds 100%.

Quotes from <"A question.......">.

cheers Darrel

I still don't get it. Oxygenation and oxidation are two different processes. Oxidation is a chemical reaction that will turn cations (Ca, Mg ) into base (CaO and MgO). Oxygenation is release of free O2 that will increase O2 concentration without necessarily chemical or pH reaction that follows.

 

[dw1305]

Hi all,

Oxygenation is release of free O2 that will increase O2 concentration

Yes, that is it. If you supersaturate water with O2 the pH will rise. <"If pH rises above pH8 (the carbonate ~ CO2 ~ pH equilibrium point)"> you know that you have another base present.

Usually oxygen (and other gases) supersaturation occurs when you have a very rapid temperature rise (dissolved gases are less soluble at higher temperatures) or when you have a very large volume of photosynthetic organisms in still eutrophic water, this could be in the <"Canford Park pond">, or possibly in aquaculture or in <"waste water treatment">.

Have a look at <"Extreme diel dissolved oxygen and carbon cycles in shallow vegetated lakes"> if you don't have access?. This is where the graph below is from. If you look at the Dissolved Inorganic Carbon (DIC or TIC) graph you can see it is predominantly an oxygen, not DIC, effect.*



* Edit - This is wrong, it is entirely a CO2 effect. Photosynthesis has both depleted the CO2 (which causes the pH to rise) and produced the oxygen (which doesn't change the pH)

cheers Darrel

 

[tiger15]

The charts show strong correlation between pH and O2 and weak inverse correlation between pH and CO2. But I wonder if scaling may distort the apparent correlation as O2 and DIC/CO2 are scaled differently by a factor of 1000. Correlation is not necessarily causation, unless it can be supported by defined mechanism. If the causation is true, oxidation of base metals must play a greater role than reduction of carbonic acid to increase pH. If true, using the kH pH chart to read CO2 is interfered by not only the presence of non-carbonic acids but also the presence of other oxidizable bases in an opposite direction.

 

[Animallover]

Just an update. I went for praecox in the end and got 4 males and 4 females. They are very fun to watch with all the flashing and are very active and will dart from one side of the tank to the other side in a flash. I think their colour is okay but my cardinals blue just stands out too much so they don’t look as flashy. I’m fully stocked now so won’t be adding any more fish. Quite happy with the end result of my first ever tank. Thanks for the help everyone.

 

[Leoki]

Silver tetra (Gymnocorymbus bondi). But some cool ones pop up when googling "Blue silver tetra"

 

[dw1305]

Hi all,

But I wonder if scaling may distort the apparent correlation as O2 and DIC/CO2 are scaled differently by a factor of 1000.

They are just in different units, the TIC (CO2 / HCO3-) is expressed as milliMol, and the dissolved O2 as microMol. One milliMol is 1000 microMols. On the graph 0.5 millimol is equivalent to 500 micro Mol.

You can convert from mMol to mg / L (= ppm) using the RMM of CO2 etc. The RMM of CO2 is 14 + (16*2) = 48, so (a theoretical) 48g of CO2 in 1 litre of water is a molar solution. A milliMol solution is 1/1000 of that = 0.048g and a microMol solution 0.048 / 1000.

cheers Darrel