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Troubleshooting pH Changes in Your Fish Tank

How Can I Figure Out Why My Aquarium pH Is Changing?

(The First Tank Guide)

If the pH is changing in your fish tank, or if the pH is different in the fish tank than it is from the tap (or other water source), you will want to try to figure out why this is happening. Once you have figured out why your aquarium's pH is changing, then you will want to correct the cause so that the change is eliminated.

Before you delve into this too far, however, you should understand testing, including normal cyclic changes in your tank and what you are testing for and why.

Possible Causes of pH Shift

The most likely causes of a shift in pH are:

How do I Tell if Something in the Water Source is Affecting the pH?

This is probably the least likely possibility, but it is also the easiest to check, so I'll address it first.

To test this, fill your aquarium bucket with water and test the pH. Then let the water sit for several hours and test again. If the pH has changed, then you know that something in the plumbing (for tap water) or the packaging (for other water) is temporarily affecting the pH and that the pH is reverting once it is no longer under the influence of whatever is changing it.

If the pH has not changed after a few hours, let the water sit for 24 hours and test again. It is even less likely that you would see a change in pH at this point, because most pH changes are very rapid - even instantaneous.

If the pH in your bucket of water has changed, you know what is changing the pH, and you can easily address the influence on your tank by just letting the water sit before adding it to your tank. With a little time an patience you can even figure out how long to let the water sit (usually just a few minutes).

However, if you are not seeing the large change in pH that you have observed between your source water and your fish tank, you will need to keep looking.

What About Something in My Fish Tank Changing the pH?

Check your aquarium for items normally expected to alter fish tank pH, like sea shells, coral skeletons, wood, peat, dead plants (including leaves), dead fish (or other animals), bones, lime stone, etc.

If you have anything obvious, remove it and see what the pH does with your next water change. It may be that some decoration in your fish tank is raising or lowering your pH, and you will want to remove that.

If there isn't anything obvious, look for less obvious things. What is your aquarium gravel made up of? Is it appropriate to your tank? Some aquarium substrates, like crushed coral, are intended only for use in marine aquarium or tanks where a high pH is desired, and can have adverse effects on aquariums where a high pH is not desirable.

If it's not the gravel, you may want to try removing decorations or other items from your tank and see if the pH is affected. you could also try removing items from the tank and putting them in your bucket of untreated tap water (from above) and see if the pH in the bucket changes over a few hours.

When checking for possible culprits in your fish tank, don't forget to test your filter media, as some filter media, such as crushed coral or peat, could affect your pH.

Testing all the decorations and filter media in your tank can take quite some time, but is probably the most likely place to find whatever is changing the pH in your aquarium. However, in the mean time, you can start checking your aquarium chemicals and additives.

What About The Chemicals I Add to My Aquarium Affecting pH?

It is definitely possible, even likely, that something you are adding to your aquarium for one reason or another is altering the pH. It is also possible that two or more additives may be reacting with each other, or that one or more of your additives is reacting with something in your tap water and causing the pH change.

First, read the labels on each aquarium additive, and see if any say anything about changing or altering pH. They may even say this in a positive tone, as though it is nothing to worry about (which it often isn't). If you find one that says it does (or may) alter pH, is it something you can live without? If so, try not using that for a while and see if your pH problems go away. If you cannot live without that additive, check into competitors' products to see if one of them may suit your needs and not alter the pH adversely. Often, you really don't even need the additive in question.

However, even if none of your additives say anything about altering pH, there is a possibility that one (or more) is.

To test this, get a bucket of your source water, whatever that is (or use the bucket of source water you already have out, if you are not testing decorations and other equipment in it), and start testing your chemicals and additives.

One at a time, add your additives to the bucket of water. Only add what is necessary to 'treat' the amount of water in your bucket. After you add each additive, let the water sit fro ten or fifteen minutes, then test the pH. If the pH hasn't changed, move on to the next additive. Keep track of which additives you are adding and in what order. Once you see your pH change, you know one of the chemicals or additives necessary to cause the pH change in our fish tank.

As I mentioned above in reference to an additive that says it may alter pH, you can choose to stop using this additive or look into a competitors' product. If discontinuing use of this additive addresses the pH problem, then your problem is solved. But it is possible tat some other chemical is also contributing to the problem, or that this additive is reacting with something else you are adding, so you may want to continue testing to see if you can narrow down te problem additives, then choose from those which to quit using.

How Do I Avoid pH Problems in the First Place?

First, keep the number of chemicals you are adding to your aquarium to a minimum, and then make sure you know what those chemicals are, why you are adding them, and that they really work. Many of the chemicals that a lot of aquarium owners add to their tank have little or no benefit, and many even have some pretty significant drawbacks. By keeping additives and chemicals to a minimum, you will probably encounter fewer problems.

Then make sure that anything you are putting in the tank won't affect the pH and is aquarium safe and suitable for use in the type of aquarium you are keeping.

This will probably keep you out of trouble with your pH, and help keep your tank happier and healthier. providing your weekly 10-15% water changes and other necessary routine aquarium maintenance will also help to keep any fluctuations in pH under control, as well as contributing to a happy and healthy aquarium in general.

It is also important to know what pH your fish actually want, and what pH range they do well in. Knowing this will help you determine whether you even have a pH problem in the first place.

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March 31, 2010
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"The info on your page has made my love for fish keeping 500% stronger as my tank is now crystal clear and my fish are full of life."
May 4, 2005
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