I'm guessing that you have arrived at this page because your aquarium water has turned cloudy? Please don't worry, everyone who keeps fish will experience cloudy aquarium water at some stage, even very experienced fish keepers will have it happen to them. If you have recently set up a new aquarium then you should be aware that they can be quite unstable for the first few weeks during the cycling process. You shouldn't worry if you do experience cloudy water. However, it's a good idea to know why fish tank water can suddenly turn cloudy, and most importantly how you can prevent it from happening.
On a more serious note, cloudy aquarium water is often the first sign that there is an imbalance going on in your tank. It can often indicate that your filtration system is not working as well as it should be. Cloudy water should be addressed as soon as you discover it.
When fish go to the toilet, breath, or when plant matter decays, ammonia is produced. The bacteria in your filtration system consumes ammonia and keeps everything healthy and clean. However, if your filters are not working properly then this bacteria will start building up in the aquarium water, when there's enough bacteria present, the water looks cloudy, we then call this a "bacterial bloom"
Algae Can Cause Cloudy Water
A very good example of when fish tanks often go cloudy is when people bring a goldfish home from the fair and put it in a bowl. This practice is hopefully quite rare now, but years ago, people didn't think that their goldfish needed any filtration. Of course all fish produce waste (ammonia) and without the means to remove this, the water will turn cloudy. We would never advocate keeping fish without filtration. However if you do happen to be keeping a goldfish in a bowl without filtration then you should change the water on a daily basis ensuring toxins don't reach lethal levels. Always make sure that you use a water conditioner to remove chlorine. Remember that goldfish are cold water fish so there's no need to add heated water.
Your aquarium water may well look nice and clear when the lights are not switched on. However when you switch them on things look a little bit murky. It may not be a case that you have any problems such as a bacterial or algae bloom, it could be as simple as lots of bubbles in the water, especially if you've got a fairly strong filtration system.
Please be aware that the introduction of new substrate such as gravel or sand to an aquarium may well result in cloudy murky water. We always recommend cleaning sand or gravel before using it as substrate, however with all the will in the world there will always be a little bit of dirt or dust still contained within the substrate which is bound to cause a little bit of cloudiness in the water. This doesn't normally last for more than a day or two so let things settle if your water has turned cloudy after adding new substrate.
Treatments for algae and cloudy water
Below is a list of some basic mistakes that should be avoided if you don't want to wake up to a cloudy aquarium
One mistake many people make, normally newcomers to aquatics is to switch the filtration off at night, probably thinking that they are saving money. This is a major mistake that will completely wipe out your biological filter overnight. You will then have to cycle your aquarium over again. So never switch your filtration off for too long.
Another big no-no is washing biological media in the sink using tap water. I would say that 90% of newcomers have probably done this at one time or another. Water companies add chemicals to their water to make it safe for drinking. As soon as you pour it all over your biological media, you kill the bacteria straightaway. Again, you would have to cycle your tank over again.
Some medications contain chemicals that are very damaging to your biological filter. One of which is which is often used to stop fungus growing on eggs. Always read instructions before adding medication to your aquarium.
Water conditioner should always be used when adding tapwater to your aquarium. Whereas small amounts won't pose a problem, a very large water change without using water conditioner could affect your biological filter, notwithstanding harming your fish. I've used all sorts of water conditioners over the years, however I would highly recommend as this stuff goes a long way so you get great value for your money. A large bottle should potentially last you several weeks of regular water changing.
Don't ignore cloudy water in your aquarium, it is a sign that there is either an imbalance somewhere, or your water may not be in the condition it should be. The best advice I can give any fish keeper is to get your own water testing kits so that you can test your water as soon as problems occur, rather than having to wait for the fish store to open.