Skip to main content

Why is my fish tank cloudy?

Why is my fish tank cloudy?
(Image credit: Getty Images)

If you're a fish owner, you've probably wondered aloud, "why is my fish tank cloudy?" It's a common question and a problem that often plagues amateur aquarium owners even when they own the best fish tank (opens in new tab). There are a few reasons why your fish tank is cloudy, and a lot of it has to do with bacteria, nutrients, and the objects you have inside your tank.

Cloudy fish water makes it difficult to see all your beautiful fish and the hard work you've put into creating a beautiful home for them. Whether you've got the best small fish tank or one of the best tropical fish tanks, you want your water to be crystal clear for you and your fish. 

While the appearance of cloudy water won't harm your fish, it can point to a chemical imbalance in the tank, which could be dangerous for your aquatic friends. Don't worry, in this article we'll answer the age-old question of "why is my fish tank cloudy" while also providing you with tips on tricks on how to fix it. 

Why is my fish tank cloudy? Everything you need to know

There are quite a few reasons why your fish tank may be cloudy. Fish owners commonly notice cloudiness in a freshly filled or brand-new tank, but there are instances where a long-maintained tank can get cloudy. We'll take you through all the main reasons why your fish tank is cloudy. 

Cloudy fish tank causes

If this is a new aquarium setup that you've started from scratch, it could be whatever substrate you're using. Substrate is the material you use to line the bottom of your tank, and many of them used for freshwater tanks are coated with epoxy – therefore you need to rinse them really well. Substrates can also be incredibly dusty, so your best bet is rinsing the substrate (usually gravel) in small amounts to ensure you get all the materials off of it.

The type of water you're using could also be contributing to the cloudiness.

Sometimes starting a new aquarium can cause something called a bacteria bloom, which can crop up days, weeks, or even months after you set up your new tank. This is a fairly common occurrence, and will usually sort itself out. Let this initial kind of bloom run its course – especially if you haven't put any fish in there yet. If you have fish in there, you'll want to make sure to increase aeration to ensure the fish are getting enough oxygen, as the bacteria will suck a lot of it up in the water. 

In an established tank, there could be a sudden increase in nutrients (perhaps a fish or plant died off and was not removed) that led to a rapid increase in a type of bacteria called heterotrophic bacteria. Heterotrophic bacteria exist to break down uneaten food, fish waste, and dead plants. 

Green water in your tank is due to an overgrowth of algae, which can be caused by too much direct sunlight on the tank or leaving indoor lights on the tank for too long. Excess nutrients can also cause algae growth, as can phosphates and nitrates. 

If your water is brownish, this could be due to the kind of decoration you added in there. Driftwood is a very common tank decoration, but if it's not presoaked before being introduced to the tank water, it will release tannic acid that should eventually clear up. As always, if your water changes in any way, test the pH level to ensure your fish are safe. 

best fish tank

(Image credit: Getty)

Why is my fish tank cloudy after water change?

There are a few things that could cause your fish tank to go cloudy after a water change. If you haven't added new substrates, fish, plants, or other objects, then it's gotta be the water. 

You could have a high level of what's called "dissolved constituents" in a freshly filled tank, which are things like heavy metals, silicates, or phosphates. You can test your water to see if this is the case – if you have a high pH, this could be the issue. 

New water introduces new nutrients, so the bacteria that causes cloudy water could be feeding off of that. You can let this run its course, keeping an eye on aeration and pH levels, as the bacteria will eventually die out once its nutrient source is gone. 

How do I get my fish tank water crystal clear?

Get a tap water conditioner to get rid of things like chlorine, heavy metals, and ammonia in your tank water. You can also buy prepackaged aquarium water that doesn't have any of those pesky items, or get a reverse osmosis system. These can be a bit expensive, but they remove contaminants from the tank water and filter the contaminant-free water back into the tank. 

If your cloudy water is due to a bacteria bloom, you can usually just let it run its course. If you want to be proactive you can increase the number of live plants to help lower nutrient levels, change the water out, clean your substrate, and reduce the amount of food – all of these things contribute to an increase of nutrients in your tank. 

In fact, the majority of cloudy aquariums can be cleared or improved by ensuring that 10 to 15 percent of the water is changed on a weekly basis, using a high-quality fish food and cleaning the gravel regularly. You can buy a vacuum to suck up any debris in your gravel, which will help keep your substrate clean. 

If your water is green due to algae, you'll want to remove the tank from direct sunlight or keep the lights on in the room it's in for less time. Increasing your amount of aquarium plants will help keep the water nice and clear, as well as ensuring that you don't give your fish too much food, as waste will contribute to the growth of bacteria. Invest in a good filtration system, and if you need a quick fix, you can get a clarifier at your local pet store. This will quickly fix a cloudy tank, but your problems will return if you haven't gotten to the root of the issue.

Keeping your fish tank crystal clear can be quite a task, but there are plenty of ways to make sure your fish are swimming through gorgeous clear waters.