my PH level going crazy or am i?

[sldp999]

hi,
i was just wondering, i have a fresh water tank with lots of live plants and a few fish.i'm using pressurized CO2. the CO2 is off in the night because plants dont absorb it in the night, they absorb oxygen. this mean that my PH level in the day is a perfect 6.7 and at night it goes up to 7.9(thats when the CO2 is off).
now, is that BAD for plants and fish? or is that normal?


PS. i'm thinking of getting 2 DISCUS fish and i hear that they high maintenance fish so will this affect them in a bad way?

THANK YOU.

 

[SpeedEuphoria]

thats normal, people usually have a full 1 point drop in PH with good CO2 levels.

Are you using a drop checker?

Whats your waters KH?

 

[DSenn]

I'm glad someone brought this topic up again. From what I have learned on here, the change in pH that is caused by the CO2 will not be detrimental to the fish, but changes in pH from alterations in KH can be detrimental. I 'assume' the pH change from an alteration in KH is more 'biological' and therefore is harmful.

What I don't understand is that I thought CO2 forms an acid, and the job of the KH is to buffer the acid. But supposedly CO2 does not affect KH, so why doesn't the acid that CO2 makes affect the KH? Confusing indeed.

 

[OasisKeeper]

Reading assignment: "Ecology of the Planted Aquarium", Diana Walstad, Chapter VI 'Carbon', Section A "Water Alkalinity, pH, and CO2". I'd quote it, but its copyrighted material and it would hardly be fair to the author. Why not see if your local library has a copy?

A short answer might be that what Kh is measuring; carbonates and bicarbonates and CO2 are all part of the same set of ion interactions in the water. When you inject CO2 you are just shifting these interactions towards the acid side. And when you stop, it just goes back to where it was based on CO2 levels in the atmosphere.

ALso, I don't think I've seen anyone say that pH swings resulting from stopping the CO2 at night are anybetter for fish then any other kind of pH swing. That is why most people don't stop injecting at night.

 

[BillD]

It isn't pH swings that are detrimental to fish but rather, swings in TDS, Total Dissolved Solids. With CO2 injection, the pH changes but the makeup of the water doesn't. The day to night fluctuation proves that. If injection continues when the lights are off, the pH will drop even lower, rather than rising which it does if injection is turned off with the lights.

 

[bs6749]

hi,
i was just wondering, i have a fresh water tank with lots of live plants and a few fish.i'm using pressurized CO2. the CO2 is off in the night because plants dont absorb it in the night, they absorb oxygen. this mean that my PH level in the day is a perfect 6.7 and at night it goes up to 7.9(thats when the CO2 is off).
now, is that BAD for plants and fish? or is that normal?


PS. i'm thinking of getting 2 DISCUS fish and i hear that they high maintenance fish so will this affect them in a bad way?

THANK YOU.

You shouldn't even think about getting discus unless you know what you are doing and have done research on them. Two is not a good number when dealing with discus unless you are purchasing a mated pair. I highly doubt that you have that in mind because the price is generally greater than $300 for a pair, much more for a proven pair. The minimum tank size for discus would be a 55 tank, which would allow you to house 5-6 adult discus. The MINIMUM number of discus that you should keep together is 5-6. I would suggest a tank no less than 75 gallons for a group of them after dealing with them and knowing that they like room to swim. They are a schooling fish and need numbers to establish a pecking order so one fish isn't constantly being picked on and stress by the other fish. Having more fish helps to spread out aggression, especially at feeding time.

If your tank has a pH swing that drastic I wouldn't recommend discus for you unless you are willing to keep the CO2 on constantly.

Plants do not absorb oxygen, I don't know where you got that information from but it is not correct. What sense does it make to absorb a bi-product that has already been released into the water?

I'm glad someone brought this topic up again. From what I have learned on here, the change in pH that is caused by the CO2 will not be detrimental to the fish, but changes in pH from alterations in KH can be detrimental. I 'assume' the pH change from an alteration in KH is more 'biological' and therefore is harmful.

What I don't understand is that I thought CO2 forms an acid, and the job of the KH is to buffer the acid. But supposedly CO2 does not affect KH, so why doesn't the acid that CO2 makes affect the KH? Confusing indeed.

A pH swing is a pH swing and one from stopping CO2 injection is no more harmful than one from a lack of KH. In fact, there is a relationship between them. When CO2 dissolves into water carbonic acid is formed and then immediatly turns into carbonate and bicarbonate ions as carbonic acid is extremely unstable. KH is a measure of the levels of bicarbonate and carbonate ions in the tank.

A short answer might be that what Kh is measuring; carbonates and bicarbonates and CO2 are all part of the same set of ion interactions in the water. When you inject CO2 you are just shifting these interactions towards the acid side. And when you stop, it just goes back to where it was based on CO2 levels in the atmosphere.

ALso, I don't think I've seen anyone say that pH swings resulting from stopping the CO2 at night are anybetter for fish then any other kind of pH swing. That is why most people don't stop injecting at night.

You are correct.

 

[bs6749]

It isn't pH swings that are detrimental to fish but rather, swings in TDS, Total Dissolved Solids. With CO2 injection, the pH changes but the makeup of the water doesn't. The day to night fluctuation proves that. If injection continues when the lights are off, the pH will drop even lower, rather than rising which it does if injection is turned off with the lights.

Not true. pH swings can be harmful to fish and can stress them to the point of death at the extreme or sudden pH changes can cause "pH burn" on the fins of the fish which can take over a week to heal.

Actually, the "makeup" of water does change with an increase or decrease in pH. pH is the level of hydronium (H30+ or commonly H+) ions present in the water. Water "self ionizes" meaning that at standard conditions, there is an equilibrium where one ion in every 10^14 molecues of water will spontaneously turn from good ole H2O into H3O+ ( which is the acidic form of water) by stealing a neighboring atom's proton. Other chemicals in the water can also provide this proton. Strong acids such as HCl, HI, H2SO4, etc, nearly ionize 100% or break down into H+ and their conjugate base. This provides an extremely large amount of free protons which water molecules will be attracted to and will form bonds with. Weaker acids (most acids are weak acids) do not provide nearly the amount of protons that stong acids do and that's why the pH of water isn't changed as radically as when something like CO2 is added to the water.

The pH of the water would not continue to lower if the CO2 injection was kept on all the time. There is a solubility constant for CO2 in water and once that amount is reached or once equilibrium is reached in the system, no more will dissolve and will simply rise out of the tank as waste. That's why you can put too much CO2 in the tank. Certain factors/chemicals can allow more or less CO2 to dissolve into the water.

 

[OasisKeeper]

Well, I can imagine a situation where you have a LOT of plants and a TON of light hitting them during the day, and these are using a lot of carbon during the day. If you adjust your injection rate to hold 30 ppm of CO2 while the plants are consuming a lot, it is possible that when they are not, the CO2 concentration will rise to levels that you may not be happy with and you will get the attendant pH fall.

This all assumes you are using a bubble counter or similar and using the same injection rate all the time it is on.

The other answer is a controller, injecting as necessary to hold a given pH and ppm CO2. But as with all things, automation = $$$.

 

[Purrbox]

1. pH swings due solely to changes in CO2 concentration are NOT harmful to fish. It's only the pH swings caused by KH that are harmful. Most people focus on the pH instead of KH simply because pH kits are more commonly sold.

2. It's very common for CO2 injection to be turned off at night. It's a great way to save on CO2 with a semi automated system.

3. Plants only consume CO2 and release O2 when they are photosynthesizing. At night when there is no light and they aren't photosynthesizing, they do consume O2 and release CO2. It's generally in much smaller amounts than what is released while photsynthesizing during the day. This is why there can be problems with low O2 levels in an aquarium that is both extremely heavily planted and overstocked with fish. At night when you have both the fish and plants consuming O2, if enough wasn't produced during the day then you end up with fish gasping at the surface by the morning.

 

[jsoong]

I might just split the difference on the pH swing thing ....

pH swings due to CO2 changes are LESS harmful than pH swings from other causes.

The whole situation is analogous to Respiratory acidosis in animals. <Respiratory acidosis is pH drop due to CO2 accumulation .. from exercise, etc ... In this case the CO2 is generated internally, but externally added CO2 has the same effect.>

Respiratory acidosis is much better tolerated than metabolic acidosis. This is prob. an adaptation to exercise. However, there is a limit to this. In people, I can push the CO2 up to 8% (from 5%), & the pH drops from 7.4 to 7.1, and there is no real problems. However, we get stress responses if I push the pH down into the 6's.

Something like that is true in fish. Although pH swings from having the CO2 off at night had not been shown to be detrimental, I would still like to minimize the amplitude of the swing (by having adequate KH, for example).

 

[OasisKeeper]

1. pH swings due solely to changes in CO2 concentration are NOT harmful to fish. It's only the pH swings caused by KH that are harmful. Most people focus on the pH instead of KH simply because pH kits are more commonly sold.

I have a really difficult time with this statement. A change in pH, a measurement of H+ ions in the water, is a change regardless of the cause. Now obviously the rate of change is also a factor, but I can't help but read this as agreement with BillD, that ph is of little consequence, compared to other factors like TDS (which I will happily agree does indeed effect fish health).

That said, I am not here to disagree (too much ), only to learn. And I know there is at least one casual study (believe its over on the Krib) agreeing with your point of view. But my core belief is that stable water parameters in the range suitable for the species being kept, is the best for fish health. Ph is no exception, regardless the cause of the change.

 

[bs6749]

I have a really difficult time with this statement. A change in pH, a measurement of H+ ions in the water, is a change regardless of the cause. Now obviously the rate of change is also a factor, but I can't help but read this as agreement with BillD, that ph is of little consequence, compared to other factors like TDS (which I will happily agree does indeed effect fish health).

That said, I am not here to disagree (too much ), only to learn. And I know there is at least one casual study (believe its over on the Krib) agreeing with your point of view. But my core belief is that stable water parameters in the range suitable for the species being kept, is the best for fish health. Ph is no exception, regardless the cause of the change.

Exactly. It doesn't matter WHAT causes the pH to change, it's still a change. It's not any safer/nor any different if the pH change and rate of change is the same.

 

[OasisKeeper]

Well, Tom Barr doesn't believe it either So I guess Joy and BillD are in good company. Like I said, here to learn. Science is better then anecdotal evidence however.

 

[Purrbox]

Well, Tom Barr doesn't believe it either So I guess Joy and BillD are in good company. Like I said, here to learn. Science is better then anecdotal evidence however.

The problem is that most aquarists are hobbiests and not scientists. Most of us are doing well to get a basic grasp of how the science works in our aquariums, and the details of the why generally are much too involved. In general you aren't going to get a good scientific experiment from an aquarist, because there are simply way too many variables to control. I personally rely heavily on information that I learn from experianced/advanced aquarists like Tom Barr.

 

[SpeedEuphoria]

1. pH swings due solely to changes in CO2 concentration are NOT harmful to fish. It's only the pH swings caused by KH that are harmful. Most people focus on the pH instead of KH simply because pH kits are more commonly sold.

This is the way I always looked at it, from what little I know, which is already brought up here to a point, its an H+ ions change/issue with CO2.

Here look at Wiki:
pH - Wikipedia, the free encyclopedia

It says

Because pH is dependent on ionic activity, a property which cannot be measured easily or fully predicted theoretically, it is difficult to determine an accurate value for the pH of a solution.

Basically the PH is a very general overview of the water conditions(that is estimated/predicted), which most of us would agree, things like KH/TDS/GH/CO2 and others will point you to a truer PH.

Tom Barr has some sound explanation of it and I'll take his word.



Funny thing, anyone else see the show on discovery, where they were talking about extracting CO2 from the air and injecting it into the Ocean/ocean floor? I was looking at similar documents on the web a week or 2 before that so I thought is was an interesting show but I didnt get to watch the full episode. In the little research I did the papers seemed concerned about the PH drop from the added CO2, I'm not so sure that they knew about aquarist that did this, also not sure if SW would be different?

Here's some info on it that I found:
http://www.ieagreen.org.uk/oceanrep.pdf
http://www.tos.org/oceanography/issues/issue_archive/issue_pdfs/14_4/14_4_feely_et_al.pdf

 

[OasisKeeper]

Heh, nice edit

Tom Barr has some sound explanation of it and I'll take his word.

I do too. The issue for me is that what he is talking about the fishes ability to tolerate such change. It doesn't really speak to longer term issue of health and what might happen when fish are stressed with daily swings. He talks about experiments he has done and infers that there are no longer term effects because the fish survive.

So short some other evidence, I have to conclude that we don't know. I certainly don't.

Common sense tells me some things though:

1) Water conditions as close as possible to the conditions the fish were raised in or caught in, would seem to me to cause them the least stress, although we know many fish are adaptable over the longer term.

2) Water condition that are the same today as yesterday, or eight hours ago are less likely to cause stress then water conditions that are changing.

So, I make keeping water conditions stable a goal. In aquariums you can never get that perfect, but efforts to improve it are often rewarded in my experience.

 

[DSenn]

Don't get me wrong. I understand that the pH changes due to CO2 addition are not as detrimental as a change in pH due to KH. BUT...

When you add CO2, it forms an acid, correct? Isn't it the job of the KH to ABSORB (buffer) the acid? Hence, the KH would be affected (decreased)?

Basically, if CO2 forms an acid, why isn't the KH affected?

 

[OasisKeeper]

When you add CO2, it forms an acid, correct?

Yes, carbonic (Edited to add: Thats what makes Soda Pop tangy)

Isn't it the job of the KH to ABSORB (buffer) the acid?

Well, it will never get unemployment compensation, but Yes

Hence, the KH would be affected (decreased)?

No

Its all Carbon, Hydrogen, and Oxygen. All you are doing is pushing the combination around by injecting the CO2.

Better? I didn't think so.

 

[DSenn]

So CO2 forms Carbonic Acid, but Carbonic Acid is NOT absorbed by the KH, and is therefore the KH will not affected? So there are acids that KH will not absorb. This makes so much sense...

 

[DSenn]

So half the people on here say a change in pH is a change in pH regardless of the cause, and a change in pH for any reason is detrimental.

The other half-and I am leaning towards your opinion Purrbox-say that a change in pH resulting from a shift in CO2 is NOT AS HARMFUL as a shift in pH from a change in hardness.

I still don't get how if CO2 forms an ACID that the KH won't be affected. Pulling my hair out here lol.