The magic of a backyard lies in the pond. The calm waters, the vigorous fish, the serene plants; everything adds a unique character that you can’t supplement with anything else. But for that to happen, they need to stay safe. That’s a little hard when your pond has a high pH that harms its inhabitants.

So, how to lower pH in pond with fish? You have to either increase the acidity or reduce the pond’s alkalinity by adding various substances or removing any algal growth that might have infested your pond.

Want the juicy details on what to do? I knew it! That’s why I prepared a nice little article for you that covers all you need to know. How about you take a peak?

What causes high pH in pond water?

Rising pH means your pond is turning alkaline; in most cases, the culprit behind that is the pond’s surroundings as they are likely to emit substances that infiltrated the water.

A pretty common cause behind high pH is toxic lime that has leaked into the pond from slabs or embankments nearby. In case you have a cement pond, please treat the cement before installing it so that it doesn’t leak anything into the water.

Not just cement, the same could happen from bricks or mortars around the pond. When it’s raining, untreated materials release chemicals into the water that affect the pond water’s pH.

One other culprit behind the rising pH is algal growth. In the daytime, algae use sunlight for photosynthesis; in the aftermath, a lot of CO2 gets ejected from the pond. That drop in CO2 levels sometimes causes a reduction in acidity, which means alkaline levels rise in the pond.

In case there is an algae bloom, you should do an absolute treatment before you try to adjust the pH of the pond.

Importance of pH for a fish pond

For our friends who forgot the chemistry classes back in school, let’s get a quick recap. pH is an indicator that ranges from 1-14 that goes from acidic to alkaline. Ideally, you want your pond to be at the sweet middle range that is 7.


However, life is not perfect, and our ponds as well. But still, a little deviation doesn’t hurt. Something like a pH of 6.5-7.6 is acceptable if any further, and you have to pay close attention.

Depending on your pond’s situation and surroundings, it is pretty easy for your pond’s pH to be altered. Too alkaline or too acidic, both are harmful to your fish.

When the pond’s alkalinity rises too much, ammonia levels rise, and your fish encounter trouble in breathing and many other hardships. If the acidity of the pond increases, the fish lose their appetite, can’t breathe properly, and become lethargic.

In case things become worse, it could also mean fatality for your fish. Lucky for you, the situation can be salvaged if you catch onto it early enough.

So don’t let things go out of your hand. As for HOW to salvage it? I’ll share that with you right now!

How To Lower pH In Pond With Fish

How to lower pH in a pond

A pond is more likely to get its pH raised than lowered. We already established what causes this kind of inconvenience. So it’s time I show you the remedy.

The core principle is simple; we gotta reduce the alkalinity of the pond or increase the acidity. It’s time I set aside the semantics and get to the point. Below I mentioned a few methods that could lower the pH of your pond to a tolerable range:

1. Remove algae

Algae is no friend of yours, nor your fishes. You need to get them out of your pond as soon as you can. If you see that your pond is too green and has a spiked pH, algae are most likely to the cause.

I always recommend using a UV clarifier for a pond, as it can remove algae and suppress any future growth. Don’t worry about safety, they are much safer than algaecides and at the same time, very effective at what they do as well. Pond filters with UV clarifier is a great option.

If you run it for a few days, your pond should be algae free. Afterwards, test your pond water and check the pH to see if it needs further treatment.

In most cases, removing algae is enough to bring the pH of your pond back to tolerable values.

2. Have a stable KH

Sudden pH spikes are not normal at all. Whenever you see this happening you should get a good reading of the KH [carbonate hardness] of your pond. It indicates how much bicarbonates and carbonates are dissolved in the water. They work as a buffer that prevents such spikes.

Ideally, you’d want your pond to have a KH between 125-200 ppm. If the result is lower than that, then you have your culprit.

The best approach here is to take things slow. If the KH level is below 125 ppm, you need to raise the concentration again slowly. An excellent way to do that is by adding baking soda every day until the KH rises.

I’m not joking! You can use baking soda to lower the pH of your pond by raising the KH. In case you want an alternative, using a KH booster is another way to achieve your goal.

Both are effective methods that’ll solve this problem. But before you start adding baking soda, be sure to check how much KH your pond is lacking to provide the right dosage. KH boosters come with labelled instructions so they got you covered.

I’ve prepared a rough instruction for those who want to use baking soda; I am a good friend, see?

Pond size [gallon]For 30 ppm deficitFor 40 ppm deficitFor 50 ppm deficit

Follow these and you won’t have to worry about putting the wrong amount at all.

3. Increase acidity

When the KH of your pond is in control and there are no algae, you should check the pH both during the morning and night. Repeat this for a few days and note the readings.

If the pH is in acceptable limits and the spikes are not significant [more than 0.8], then you’re good to go, you don’t need to lower your pH.

However, even after all that if the pH is still 8.5 or above, you need to add some stuff. A few “pH down” products in the market slowly increase the acidity of your pond to lower the pH.

They are tested to be biosafe, so the fish won’t suffer because of these. A slow decline in pH is better than a rapid one, and these products only lower the pH by 0.2-0.5 per day.

After dosing, re-check the pH of the pond in 24 hours.


Never lose heart, remember your pond water is always treatable. If one method doesn’t work, try another. But for the sake of your fish, please don’t stop.

I am confident this article will give you enough assistance and you won’t have to ask anyone else about how to lower pH in pond with fish ever again.

Good luck keeping your pond healthy and safe! They deserve the best.

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