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Treating pH shock in Fish

pH shock

A guide to identifying and treating pH shock in fish.

pH shock

Shock in fish can be very dangerous, and in many cases, lethal to them. Fish don’t do well with shock and will quickly become very sick from it. pH shock is no different to any other kind of shock and can very quickly be deadly to your fish, though it is worth noting that pH shock is actually fairly rare.

Each species of fish has a preferred pH that they are comfortable in, some have a wider tolerance than others, but all have their limits. Despite this, fish can live in pH levels outside of their ideal range, they won’t be particularly happy but as long as the pH is stable, they will often survive. However, it is always best to keep a fish within its recommended tolerance range.

Whilst some fish will tolerate life outside of their optimal pH range, sudden changes in pH will send some fish into shock. Much like a sudden drop in temperature, large, quick changes in pH can be instantly lethal to fish.

Changes as small as 1 pH can send fish into shock. Some species are hardier than others and some will therefore cope with changes better than others, but in general, any large, sudden change of your pH will cause some level of shock in your fish.

This isn’t always the case though and this is proven by CO2 injection. Planted aquariums with injected CO2 systems have fairly large, daily variations in pH. This is due to CO2 being acidic. Yet these tanks are often populated with fish that have seemingly no issues with the regular changes.

So, if you think your fish may be suffering from pH shock, it is worth checking other parameters too to rule them out first.


Causes of pH shock

pH shock is caused when the pH of the water in the aquarium suddenly changes. A common example of this is when you first bring fish home. Your pH may be very different from the pH of the water used in the shop. This means that when your new fish enters your tank, there is a large, sudden change in pH, which causes shock.

Another example is when adding wood to an aquarium. Aquarium wood can lower pH, usually this is gradual but if you add a lot of new wood at once and have low KH, the change can be quick enough, and large enough, to cause pH shock. I came across just such an incident earlier this week which I’ll show you more on below.


Old tank syndrome

Like new tank syndrome, old tank syndrome is pretty common and is another reason that your pH can change. Over time, the KH (alkalinity) value of your water can drop, this means that the waters ability to buffer, and therefore keep a stable pH, is diminished. This can cause a drop in the pH of your aquarium causing it to acidify.

The solution to this is relatively simple and prevention is always better than the cure. Regular maintenance and water tests are the best method of prevention. Regular testing will enable you to notice early on if your parameters are changing, but regular water changes should prevent that from happening as the new water replenishes your KH value.

If you are unlucky enough to be struck by old tank syndrome, you will need to perform small, regular water changes (10-15% daily) whilst regularly testing your water. Doing a large water change may have a similar effect to pH shock on the wellbeing of your fish, as the water conditions will change too quickly after having been degrading for a while. (This is different to the treatment for a sudden change, which I will cover below).


Signs and symptoms of pH shock

The signs and symptoms of pH shock are very similar to those of any other shock in your fish. There is though, one thing that will tell you that pH change is the cause of the issue. This is one of many reasons that regular tests are a must. Testing the water will show you quite quickly that the pH has changed since your last test. Even with a mature aquarium, testing at least once a month will help you a lot in identifying issues.


pH shock Trump the red texas

Symptoms in fish:

Flashing or twitching – The fish will ‘flash’ (sudden movements, often rubbing against objects in the aquarium or against the substrate), they may also dart around the tank sporadically.

  • Loss of appetite- Fish suffering from shock will often refuse food.
  • Swimming near the surface
  • Gasping – Shock can make it difficult for fish to breath, so they will appear to gasp for breath.
  • Lethargy – Fish, when not darting or flashing will appear quite lethargic with the dorsal fin dropped, often resting on the bottom of the tank.


This week I came across a fish on social media who was having just such an issue. Bogwood had been added to his tank which caused a large enough drop in pH to send him into shock. Below is are two short videos of Trump the red texas Cichlid, showing many of these symptoms.









Luckily, Trump survived and is now doing very well again. This is because the issue was caught quickly and Trumps owner sought all the advice they could to help him. As you can see though, he was not a happy fish.

Trump the red texas has his very own Instagram page, you can find it here, give him a follow to keep up with his progress!



Treating pH shock

If you are unfortunate enough to have fish suffering with pH shock, you will need to rely firstly on the hardiness of the fish, along with a little bit of luck. But there are things that you can do that will certainly help:

Firstly, you need to get your water back to within the fish’ ideal pH range. Despite the fact that this is another, equal change in pH, your fish is more likely to settle down a little if the water is returned to the state that it was previously comfortable in. You can do this by moving the fish into another tank, or by doing a large water change.

You will also need to remove the source of the problem, if possible. So if the pH change was caused by the addition of aquarium wood, coral sand, or anything else, remove it to prevent the issue from continuing.

Add oxygen. This can be done with the addition of an air pump, or by increasing surface disturbance. When fish appear to gasp, that is exactly what they are doing. Shock can often make it difficult for a fish to breath, so adding more oxygen to the water will help them a lot. Gas exchange occurs at the water’s surface, so disturbing it with a stream of bubbles, or your filter’s flow will increase the waters oxygen content.

Catch it quick! In order to successfully save your fish from pH shock, or any shock for that matter, you will need to catch it very quickly. Shock can be lethal to fish very quickly, so the quicker you can improve the fish’ situation, the better.


Prevention of pH shock

As always, prevention is always better, and far less risky, than the cure. pH shock is fairly easy to prevent, good routine maintenance is key (water changes) and always check any items before adding them to your tank. A quick spot of research will soon tell you if what you’re adding could affect your pH, so always check before you add it.

Wood and coral sand are two very common examples of aquarium items that will affect pH.



Changing pH safely

If a situation occurs where you need to change the pH of your aquarium, such as realising you are keeping your fish outside of their optimal conditions, then it is possible to safely change the pH of your aquarium water.

Whilst some fish will tolerate an instant change, some won’t, so it is ideal to change pH slowly over several days, a rate of change of 0.5pH changes per 48 – 72 hours should be fine for most fish, however, the slower this change is, the safer it is.

Natural items such as drift wood, peat moss and coral sand can be used to adjust your pH, but it is difficult to measure how much they will change it by. When adding them, do so slowly in small bits and measure the change as you go. Shop bought products are also available to adjust the pH of your water, but use them carefully and always read the instructions, as the effect of them can be drastic.


Please note that you only need to adjust your pH if it appears to be causing your fish some distress. If your water is just outside of the optimum range for your fish, but is stable and they seem happy, then it may well be a lot safer to leave your pH outside of the optimal range, but stable.



Trump recovered:

So, just to lighten the mood at the end here, here is a video of Trump the red texas, happy and eating again:



If you are struck by pH shock, then I wish you the best of luck in saving your fishy friends. Fingers crossed they pull through as quickly as Trump did!



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About the author

James @Seriously Fishy

I am a fish keeping enthusiast with over 20 years experience. I currently keep American Cichlids (CA) which are my favourite fish to keep so far. I started Seriously Fishy as I noticed a large volume of people on various web pages looking for help with Aquarium basics. I created the first Seriously Fishy book to solve the issue in 28 pages, that led to the Seriously Fishy UK fish forum and blog.

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