# How much pH fluctuation is okay over a day?



## DBridges (Sep 22, 2009)

Hi all,

The pH in my tank is about 7.5 or so before the CO2 turns on in the morning, and is about 6.6 when the lights go out. I've been running an airstone at night, and I have a powerhead that creates a little surface ripple, so I think I get enough water movement at the surface to have good oxygenation. So I guess I have two questions:

1. Is that too big of a fluctuation to be safe?

2. What is a decent duration of time to run an airstone for at night? I've been running mine for about 5 hours each night.

David


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## BBradbury (Nov 8, 2010)

*Your Qs*



DBridges said:


> Hi all,
> 
> The pH in my tank is about 7.5 or so before the CO2 turns on in the morning, and is about 6.6 when the lights go out. I've been running an airstone at night, and I have a powerhead that creates a little surface ripple, so I think I get enough water movement at the surface to have good oxygenation. So I guess I have two questions:
> 
> ...


Hello Dave...

The pH scale is "logarithmic". This means even a very small change in the scale changes the tank water dramatically. Even if the change happens in hours, your fish could be harmed severely or even die. It's best not to ever try to change the chemical makeup of your tap water. Just gradually work up to the point you change half weekly and use a treatment that removes chlorine and chloramine.

Air stones are really a nonessential. They do nothing beneficial for the tank. Your filter system is designed to move the water's surface to mix oxygen into the water and allow carbon dioxide to escape. The air stone does this too. Too much water agitation will remove more carbon dioxide and your plants won't grow as well.

B


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## Lyana (Aug 4, 2014)

Correct me if I'm wrong, but i think the ph difference created by adding co2 isn't the same as changing the water and getting a swing of that much.

I have blue rams and shrimp in my planted tank and it goes from 8.2 to 7.2 everyday without harm to the critters.


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## cmbranch13 (Mar 17, 2013)

A pH drop of 1 with co2 is usually a good target. As long as the fish don't appear stressed, you should be alright. If you really want a good answer measure the kh and use the table you can find on Google to check the co2 concentration. 15-30ppm is a good target. 

Sent from my SGH-M919 using Tapatalk


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## DBridges (Sep 22, 2009)

I guess these responses sort of illustrate why I asked the question. There seem to be two camps:

1. The fluctuation is potentially diastrous - avoid it:

2. Fluctuation is not so bad as it was once thought, especially if due to adding CO2. Keep it within a degree or so and you're fine.

As it is, my fish are doing fine and the plants are growing great, but only recently have it started monitoring continuously with a Milwaukee pH meter I picked up.

I'm leaning toward the second camp listed above being more correct, given observed results in my tank, but I'd love to know a little more of the science and biology behind it without having to read any thesis or anything.

David


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## bsantucci (Sep 30, 2013)

pH drop from co2 is definitely not the same as a pH swing from gH or kH changes. The daily co2 swing won't harm any livestock. As long as fish aren't gasping you're all good.


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## jrill (Nov 20, 2013)

bsantucci said:


> pH drop from co2 is definitely not the same as a pH swing from gH or kH changes. The daily co2 swing won't harm any livestock. As long as fish aren't gasping you're all good.


+1 for what said here.


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## Hoppy (Dec 24, 2005)

The pH is always a result of something else. It is not a primary parameter. If you add an acid to your water the pH will drop. If you add an alkaline substance the pH will rise. If the acid or alkaline you add is harmful to the fish it is that which hurts the fish, not the pH. Adding tannins, which are acidic, doesn't harm the fish, but adding inorganic acids may well harm them. When we add CO2 to the water, a tiny bit of the CO2 forms carbonic acid in the water, dropping the pH - actually it, along with the carbonates in the water, form a buffer that holds the pH constant at the value determined by how much CO2 is in the water and how much carbonates are in the water. The change in pH caused by the addition of CO2 does not harm the fish, but too much CO2 in the water will harm the fish, no matter what the pH is.

Fortunately, it is almost impossible to make really sudden changes in pH by adding CO2. Those changes take at least 10+ minutes for the pH to change even in small tanks. I think the ease of measuring pH has caused us to vastly overemphasize pH as a meaningful parameter. I never measure pH in my tank, and haven't done so for several years now.


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## klibs (May 1, 2014)

bsantucci said:


> pH drop from co2 is definitely not the same as a pH swing from gH or kH changes. The daily co2 swing won't harm any livestock. As long as fish aren't gasping you're all good.


+1

My pH swing is from about 7 - 5.9 every day. Fish are totally fine.


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## DBridges (Sep 22, 2009)

Thanks for the responses, guys. That helps to clear things up a bit.

Seems like any hobby you get into deep enough, you start to miss the forest for the trees sometimes.

David


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