There are a number of potential reasons why the water in your aquarium is cloudy; however, the most frequent causes of cloudy water can be narrowed down to a chemical imbalance in the water, algae and green water, bacterial bloom, and even debris from your gravel or plants.
The first time you set up your aquarium and add new plants as well as gravel or sand is often when you see the biggest algae growth. It is recommended that you wash these items before adding them to your aquarium or tank since it is likely that they have accumulated a lot of dust or have some loose particles on them that need to be washed away. It is very simple to accomplish this task; all that is required to clean plants is a light rinsing in some water. On the other hand, in order to clean gravel or sand properly, you must first thoroughly wash it in a container or bowl and then carefully filter the water through the material until it is clear. If items like pebbles or plants are the cause of your hazy water, the cloudiness will often only persist for a day or two until it settles down in the bottom of the tank, and it should not be hazardous to your fish in any way.
If the water in your tank has a hazy appearance that is grey or white in colour, this may be an indication that there is a bacterial bloom present. This is totally safe for your fish, and it is just the result of an imbalance in the bacteria that are present in the water and the waste and debris that are present in the tank as a result of the fish and any plants that you have. This is often something that will work itself out on its own as the tank ages, and it is typically just a problem with tanks that are quite new. If you want to get rid of it more quickly, a partial water change of around 20 percent should speed up the process. Additionally, eliminating waste and uneaten food from the tank (as well as avoiding overfeeding!) can help reduce the amount of waste that is mixing in the tank.
The presence of a chemical imbalance in the water is yet another potential explanation for the haze’s greyish hue. The presence of a greater number of minerals in the water or the addition of a significant amount of chemical additives are two possible explanations for this phenomenon. The use of a water conditioner, which helps reduce hazing by binding metal elements, may be helpful in this regard; periodically changing the water will also be helpful in this regard. However, you should examine the pH and hardness of the water that you are adding to your tank to see whether or not it might be the source of the problem. A typical contributor to chemical imbalances is the presence of gas bubbles in the water, which may be readily remedied by letting the water stand for some time so that it can reach room temperature at its own pace.
Even though there will be a dense cloud of green algae in the water, the fish will not be harmed in any way by the presence of algae, which is a typical issue in fish tanks. However, this does mean that you won’t be able to view your wonderful fish. It is possible to remedy this situation by ensuring that the tank is kept out of direct sunlight, limiting the amount of time that a light inside the tank is on to no more than 12 hours per day (as doing so may encourage the growth of algae), and changing the water on a regular basis in order to reduce the amount of nutrients that are providing fuel for the algae. It is common for this to be the underlying source of the algae, and if you adhere to these methods, you should be OK. However, in the short term, things like UV filtering or a diatom filter may be helpful. On the other hand, if the issue persists, you could have to relocate your tank or have a look at the filtration system and make adjustments to it.