Ph Changes And Co2 Injection...

[jnms]

I am currently injecting CO2 into my 200ltr tank. I use 2 bottles of yeast based mix to create the CO2 and it is 'injected' through a Interpet PF3 which mashes the bubbles up real fine and distributes them through the entire tank. I regularly change the mix, and the output is fairly consistent.

Now here is the deal. My Ph without CO2 is at around 8.1 - once the CO2 is added the Ph drops to about 7.4 and stays there. That's fine.

I keep the CO2 on 24hrs a day.

Ok, so some people switch their CO2 off at night. Naturally this means the Ph will rise during the night. Then in the daytime the CO2 comes back on and the Ph drops.

This seems in total contradiction to the whole theory of 'stable Ph'. Now I am told from reliable people over at UKAPS that this change in CO2 is not a problem. And to be honest I am inclined to trust them. However, I really have trouble getting my head round this, because it is opposite to everything I have learned about fish keeping.

Ph shock is where the fish is exposed to sudden changes in Ph. With the CO2 the Ph changes over the course of maybe an hour or 2. This change will happen a minimum of twice in a 24hr period if the CO2 is switched off at night.

Many people use DIY CO2 and this may well cause the Ph to change even more often.

Yet in all of these cases it never seems to affect the fish. So - what is the deal with Ph changes in the fish tank. Are regular (as more than once a day) slow changes ok? Or should the Ph be kept consistent?

 

[aaronnorth]

Ph shock is where the fish is exposed to sudden changes in Ph

Exactly, if we had a tank with a ph of 8, then we decided to add tap water with a ph of 6.6, this is a sudden change. However CO2 injection slowly lowers the ph so the fish are not affected, even in the wild the ph can change slightly.

 

[jnms]

Ph shock is where the fish is exposed to sudden changes in Ph

Exactly, if we had a tank with a ph of 8, then we decided to add tap water with a ph of 6.6, this is a sudden change. However CO2 injection slowly lowers the ph so the fish are not affected, even in the wild the ph can change slightly.

This is what I thought - and sorry to bring this up again aaron, you probably saw me mention it elsewhere.

So - non-sudden changes in Ph are okay even for the most sensitive of fish like discus?

 

[aaronnorth]

So - non-sudden changes in Ph are okay even for the most sensitive of fish like discus?

Yes, most fish are adaptable to ph, mainly the ones we use in a planted tank as they prefer the acidic water that CO2 injection gives.

 

[jnms]

Ok thanks aaron.

I am wondering then, where the notion came from that fish need a non-changing Ph...

 

[OldMan47]

Jnms, I think it came from people who could only test for pH. Back when I started in this hobby that was almost anyone. We only tested for pH and used strips to do it. If you go from soft water that often has a low pH to hard water that often has a high pH, it will cause the fish some significant distress. Adding CO2, won't affect the mineral content of the water very much so it won't affect the fish much. The pH of itself does not seem to have the kind of effect that people usually worry about but changing the overall chemistry of the water does hit the fish pretty hard.

 

[Bignose]

Exactly, if we had a tank with a ph of 8, then we decided to add tap water with a ph of 6.6, this is a sudden change. However CO2 injection slowly lowers the ph so the fish are not affected, even in the wild the ph can change slightly.

It's not even "slightly"; In the wild, the pH can fluctuate greatly and quickly. For that matter, in the wild, fish will sometimes intentionally go through pH gradients to take advantage of the different conditions.

I have many examples. A body of water, such as a pond or small lake, will can change well over 1 pH unit throughout a day. The sun comes up and warms the water. The temperature effect on the pH is substantial enough, but if the body of water has a lot of vegetation too, the plants will become active with the sunlight and change the pH through their activity too.

During a quick rainstorm or monsoon season, bodies of water swell up to many times their original size. The pH of rain water is usually very different than the pH of the water that is in the waterways. Yet, there aren't fish kills after every sudden rainstorm, even though the swelled body of water can have a pH that is several units different.

Finally, there are fish that take advantage of the temperature gradients in bodies of water. Where there is a temperature gradient, there is a pH gradient -- the two go hand in hand. There are fish who feed off the bottom of the body of water, which is cooler, and then travel to the top of the body or near a thermal to digest. If it was so stressful for a fish to go through these gradients, why would they do it intentionally.

Because search is broken, I can't find it really quick, but I've posted before some simple calculations based on numbers from the literature. The fact is that a fish can change its internal pH 4 units in the span of an hour. That's even using very conservative values. If you use the values posted, it is 5 pH units in one hour.

"pH shock" itself is really a misnomer. It isn't changes in pH that usually do fish in, but changes in hardness. Again, search isn't working, but I've posted a lengthy post about how the changes in hardness are the really hard changes for a fish to handle. It all has to do with the ion-exchange and charge balance and diffusion gradients that a fish uses to regulate it's internal chemistry. Usually, hard water has high pH and soft water has low pH. Not always, but usually. So, when we get home and put our fish in hard water when the shop had them in soft, we blame the pH difference because of the misconception. The fish did undergo both a large change in pH and a large change in hardness, but most people would blame the pH. Partly it's because pH is this mysterious thing that people don't understand well. We may not understand hardness really well, either, but we at least have a better idea of what it is. Also, we are always told "A one unit change in pH is really a 10 times change!" and thinks "That's so large!" So, it seems like such a mysterious and strange thing, so it must be that that killed the fish.

But, pH all in all is really a pretty minor water stat. I personally would be much more concerned about temperature and hardness. And of course, zero ammonia and nitrite. These slow changes in pH from the CO2 injector aren't bad. The fish can easily adapt to those slow changes. And, the hardness and temperature of the water are going to be the same, so it won't really matter.

 

[jnms]

Thanks for all the info - that clears things up very specifically. Monitoring the pH has always been one of the things I have worried about all the time. Nice to know I can relax a little on that issue.

 

[keenonfish]

You should have a link to your thread because I would love to fully understand Ph, hardness and all of that but have yet to find a simple writeup that gets this across in laymen terms!

 

[Bignose]

You should have a link to your thread because I would love to fully understand Ph, hardness and all of that but have yet to find a simple writeup that gets this across in laymen terms!

I'll link to it as soon as search is fixed. I'm not going to look through all 1300+ of my posts to find it.

 

[aaronnorth]

Thanks for the info Bignose, i thought i have read somewhere that ph fluctuations are quite large, but i wasnt sure so i just covered myself

Thanks

 

[jonnyf84]

this clears up a few questions i was going to have in the not to distant future. The tank i'm currently cycling is going to have pressurized CO2, now here in Leeds the water has a KH of 0.5-1 dH and can't hold a stable PH for more than a few days, it comes out the tap at a PH of around 7.2 so with CO2 injection it will drop roughly 1 point to 6.2.
I have to do a weekly water change here as if i dont i will have a ph crash that is so severe the nitrogen cycle will stall so my querie was that when i do a 40% water change and put the 40% 7.2PH tap water into 60% 6.2PH tank water the overall increase in the space of a few minutes will be roughly .5, i know this change over the course of a hour will not harm the fish in any way but in a few minutes i was not too sure. However if what Bignose says is true then the PH change should be fine as appose to my original plan. This was to up the tank PH over a couple of hours using baking soda to match the PH of the tap water, this would of coarse increase the tank water hardness as well as PH and therefore, apparently, do harm to the fish.

I will look forward to reading your post Bignose, you have me intrigued.

 

[saz326]

Just to add another spanner to the well oiled workings -

Plants not only produce oxygen during the day , but also produce carbon dioxide during cell respiration (oxygen is produced by photosynthesis, and co2 produced by cell respiration)...

During the day, the plant uses more co2 than it produces, having an overall effect of increasing the water oxygenation.

At night, plants only produce co2 (no light = no photosynthesis).

So should people ever leave their co2 systems running overnight? Is there a chance that in highly planted tank with a low surface area and little surface aggetation the level of CO2 could either lower the pH HUGELY - or cause suffocation of poor mr fishy?

side topic I know. Dont shoot me - just had to throw that spanner in.

 

[aaronnorth]

So should people ever leave their co2 systems running overnight? Is there a chance that in highly planted tank with a low surface area and little surface aggetation the level of CO2 could either lower the pH HUGELY - or cause suffocation of poor mr fishy?

The water can only hold so much dissolved CO2, so the ph will never drop a huge amount, usually by about 1. It is possible to gas your fish, but when we inject CO2 24/7 (pressurized system) we usually use a lower injection rate/ lower bubbles per second to make sure we dont cause this problem, on fermentation kits that run 24/7, it is very hard to achieve a high level of CO2.
If you are worried, then put an airpump on a timer to come on for the night, but i wouldnt worry too much.

 

[Kombat]

So should people ever leave their co2 systems running overnight? Is there a chance that in highly planted tank with a low surface area and little surface aggetation the level of CO2 could either lower the pH HUGELY - or cause suffocation of poor mr fishy?

The water can only hold so much dissolved CO2, so the ph will never drop a huge amount, usually by about 1. It is possible to gas your fish, but when we inject CO2 24/7 (pressurized system) we usually use a lower injection rate/ lower bubbles per second to make sure we dont cause this problem, on fermentation kits that run 24/7, it is very hard to achieve a high level of CO2.
If you are worried, then put an airpump on a timer to come on for the night, but i wouldnt worry too much.

I've always heard that ideally you should turn off the CO2 when the lights turn off since the plants will no longer be using it, and thus it will build up in the water and lower the pH. But it would only be a slight decrease I would think. I never had a problem when I was injecting CO2 and leaving it on at night.