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Troubleshooting Common Pond Water Quality Issues

Issues like excessive algae growth, murky water, low oxygen levels, ammonia and nitrite spikes, and pH imbalances (unfortunately) quite commonly happen in our ponds. These problems affect the health of fish, plants, and other organisms that call the pond home. In this article, we look into the solutions for these issues.

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Common pond water quality issues and solutions

Algae blooms in my pond

Ah, the algae blooms – it’s a head-scratcher for even the most seasoned pond enthusiasts. Picture this: your once clear pond water turning a vibrant shade of green or brownish seemingly overnight. Don’t worry, you’re not alone in this.

Take a good look at your pond. If it has a bold green tint and the water seems a bit murky, you might have an algae invasion.

It’s time to act quickly. Don’t feed your fish, and scoop out any remaining feed if they didn’t eat it all. Introduce some aquatic plants – they’ll compete with algae for nutrients and sunlight.
Consider using aeration systems and even UV filters. Aerators promote gas exchange, as well as water movement. UV filters will kill some of the algae.
For effective prevention it’s important to look for early signs of algae and act quickly. You may see some strings attached to the surfaces in your pond, the surfaces may become slimy.
Here you’ll find a whole article about how to prevent algae blooms in your pond.

Water in my pond became murky or cloudy

Ever looked in your pond and saw… Well not much, because the water wasn’t clear? If it isn’t an algae invasion, other reasons for that can be fine particles suspended in the water column. Reasons for that issue can be plenty.
If it is a new pond, it may just be imbalanced but give it some time and it should be fine. If the water doesn’t clear up after some time (let’s give it a week or two), depending also on the temperature and assuming there are no fish inside), it’s time to act.

Well, it’s pretty simple – water isn’t clear. 🙂
Crucial here is the color and from what I saw also size of the particles – if it’s green-ish and besides a “cloud” of fine particles, there are some clumps or strings swimming around, you most likely have an algae problem. If it’s just a cloud of fine particles, there may be different issues.

First question – do you have a filter? If yes, maybe it got dirty and it’s time to clean it up. Other reason could be that it isn’t big enough for your pond and is just not able to filter all the water volume efficiently. Click here to find out how to choose a proper filter for your pond. Another option could be that it filters out mostly the bigger particles, and the fine ones go through without problems. Make sure to include e.g. sponge in your filter, where water goes through it after the bigger particles are filtered out.
If you don’t have a filter, consider getting one if the problem persists. Filters are like the guardians of clarity, and beneficial bacteria are the cleanup crew, filtering out and breaking down stuff that clouds your water.
Keep soil from flowing in e.g. after watering or rainfall. Aquatic plants are big helpers here.

Low oxygen levels in my pond

Lots of fish, loads of organic leftovers, they are all using up the oxygen. If you have plants, they can definitely contribute to a good oxygen saturation in your pond, but only during the day, as photosynthesis – the process that plants use to turn light from the sun into chemical energy in the form of glucose, while releasing oxygen as a byproduct. 

Suspicious that your pond is going for a low-oxygen swim? Watch for fish going to the surface, trying to gasp for air. If this is the case, you need to act quickly. Some fish like koi and goldfish may be able to withstand low oxygen levels for some time but not forever!
There are also tools that help you measure oxygen levels, like this one (it also measures pH and temperature).

Keep fish numbers in check and clean up excessive organic debris. Aquatic plants can definitely help to keep good oxygen levels, however only during the day. If you don’t have many fish in your pond, it should be more than enough to survive until morning.

I am a big advocate for aeration. Be it an air stone, a waterfall, even a fountain. With that you can prevent not only low oxygen levels but also other troubles, like described above.

Ammonia and Nitrite Spikes

Fish are really awesome to have in a pond but they come with baggage – waste. This, together with uneaten food and organic material are sources of ammonia that is toxic to fish, as well as (also toxic) nitrite that is made by nitrifying bacteria from ammonia. Luckily, there is another type of bacteria, that turns nitrite into nitrate, that is far less toxic than these two above and is tolerated by fish even in higher amounts.

Fish are nervous, going to the water surface, gasping for air. Their gills get darker – this is a very alarming sign of higher nitrite levels being present in your water. Here you can read more about nitrite toxicity.
Do an ammonia and nitrite water test to see how bad it is. Such quick tests like these below are perfect for that:

Don’t overstock the fish party and be cautious with feeding. Regularly scoop out debris and uneaten food, and consider adding more beneficial bacteria to your pond. And remember, routine check-ups (read: testing) are essential!
If you are just starting your pond, make sure to read this article before you consider adding your fish.

How do I know if my water pH is right?

pH is the measure of how acidic or alkaline your pond water is. Fish and plants can be picky about pH levels. Too acidic or too alkaline, and they can start to suffer. Fish might get stressed, and plants might refuse to grow.
Everything around plays its part: soil runoff, decomposing matter, even the rocks in your pond. Rainfall can swing the pH too. These factors join forces to nudge your pond’s pH off balance.

Are your fish looking a bit off-color? That might be a hint. But there’s no need to guess – pH testing kits are here to help.

Think of buffering agents as your pH’s bodyguards. Use them regularly. And because your pond is unique, test the pH regularly too. It’s like giving your pond a health check-up.

In addition to pH, there are also two more parameters that can keep it stable:

GH and KH: the unsung heroes of pH control

They definitely aren’t mentioned as often as pH is, but they play a big role in keeping pH levels stable.

GH – General Hardness
measures the concentration of minerals in your pond water. It’s mostly calcium and magnesium, which fish and plants need. If GH is too low, the water can be too soft, making it prone to pH fluctuations. But if it’s too high, it can clog pipes and filters with mineral deposits.

KH – Carbonate Hardness (the pH stabilizer)
It is also known as temporary hardness. It is the concentration of bicarbonate and carbonate ions (HCO3- and CO3^2-) in water. It plays a crucial role in stabilizing pH levels in aquatic environments. When these ions are present in sufficient amounts, they act as buffers, helping to resist drastic changes in pH by neutralising acids and maintaining a more stable pH range.

To check the levels of both, you can use quick tests, like these below:

Problems like algae blooms, cloudy water, low oxygen levels, ammonia, and nitrite spikes, as well as pH imbalances, can impact fish and plant health. Addressing these issues often requires quick action and practical solutions. Regular testing your water and observation of changes your pond are key to preventing and resolving these challenges.

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