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    Why is My Aquarium Water Cloudy?

    Why is My Aquarium Water Cloudy?
    • Diagnose Cloudy Aquarium Water
    • Cloudy, Green, Brown, etc.
    • From our on-staff Marine Biologists
    That Fish Place - That Pet Place experts go over the symptoms and fixes of cloudy aquarium water. 



    We often receive questions about fixing cloudy water in a hobbyist's aquarium or the water appearing to turn a different color. While not all environments have crystal-clear water and a slight tint to your tank isn't necessarily a bad thing, water that is noticeably “tinted” or cloudy can be a symptom of an underlying issue in your aquarium. The color of the water can tend to point to a certain problem even if you haven't yet tested the water quality. In fact, it may even be telling you what exactly you should test for next!

    Why is my aquarium water green?
    This is probably the most common and the simplest to diagnose. More often than not, green water is the sign of an algae bloom. Algae-eating fish or other critters won't usually eat this type of algae. The algae, usually a single-celled form, is suspended in the water. The most common cause I see for these blooms in aquariums especially is high phosphate levels and this will be the first test I will always recommend. Phosphates come into the tank most often from the source water; if your water source is well water especially, phosphates may have leeched in through the soil or through nearby farms or gardens where fertilizers may have entered the groundwater. The phosphate levels may not be high enough to affect our health but in the aquarium, they can build up to levels where they are fertilizing the algae blooms and possibly causing other issues to sensitive fish and invertebrates. If you suspect this may be happening in your aquarium, grab a phosphate test kit to test both the aquarium and your source water. If the source water has phosphates, switch to a different source like RO (Reverse Osmosis) filtered water. Filter media can also help remove the phosphates already in the aquarium and regular small frequent water changes with phosphate-free water will help cut them down.

    Another cause for green water may be lighting although this will affect algae on the surfaces of the aquarium as well as the water itself. If the lights on the aquarium are on for too long (over about 8-10 hours per day), this may be overfeeding the algae naturally in the water. Also, if the bulbs are older than about 6-8 months, the spectrum (“color”) of the light itself will degrade to a more yellowish color that isn't as useful to healthy plants but will still feed the nuisance algae. Try decreasing the duration of the lights or getting new bulbs if either of those apply. If the bloom still hasn't gotten better, test the phosphate!

    Why is my aquarium water cloudy?
    This is the other very common colored-water question. Usually, the water is white and milky. Whenever we hear this, the next question will always be “How long has this tank been set up with fish?” or “Have you restarted this tank lately (removed more than a third to a half of the water)?” A milky white cloudy water color to the water is a sign of a bacteria bloom which usually happens during the Nitrogen Cycle Cycling Process of a new tank or if a tank is becoming reestablished after a large water change, medication cycle or other event. This cloudiness will usually clear up on its own; try to resist the urge to do water changes since this will only make the Cycle last longer and take longer for the bacteria population that needs to grow to take care of this on its own. You can test the water during this time to make sure everything else is normal, keeping in mind that while a tank is Cycling, you may see spikes in Ammonia and Nitrite.

    Why is my aquarium water yellow?
    Yellowish water is usually simply dirty. This is usually a result of overcrowding or overfeeding and may also be a sign of harmfully high Ammonia and/or Nitrite levels. Test the water to see if this is the case and take a good look at the stocking levels of your tank compared to its size and filtration. If you have four goldfish in a 10 gallon aquarium, it is overcrowded and the waste they produce is polluting the water. If you have two large Oscars in a 55-gallon tank with one small power filter, it is overcrowded and underfiltered. Take a look at your feeding routine too; you may be feeding the tank more than it needs and the leftover food (or the waste the fish produce after pigging out) could be fouling up the water. To fix this cloudiness, consider getting a large tank or cutting back on the fish you have in it, invest in a larger, more powerful filter, and consider if you need to feed the fish less. A filter media with carbon or another chemical neutralizer can help remove the organics that are polluting the water as well.

    Why is my aquarium water brown? This one straddles a fine line. There are some environments known as “blackwater” systems where this is actually a good thing and completely natural. These environments are usually in forested areas without a lot of water flow. The leaves, wood and other organic matter in the water releases a substance known as tannic acid that dyes the water brown...this is the same thing that makes the tea you drink turn brown. Some fish that live in these environments actually need this kind of water chemistry and there are additives and materials available to help aquarists create this kind of system. If you don't have these fish and don't want a blackwater tank however, it can be an unsightly nuisance. This usually “accidentally” comes about from driftwood in the aquarium that hasn't been properly pressure-treated or is too soft and replacing that wood will get rid of the source of the color. Carbon in the filter will help with this as well to remove the color and organics from the water. Keep a careful eye on the pH if you are seeing your water turn this tannic brown to make sure that the acids aren't lowering your pH too far. 

    These are the most common questions we get about the color of the water in an aquarium. If you are seeing a different “color” or if the solutions here aren't resolving the problem in your tank, give us a call or comment below and we'd be happy to help you figure it out!

    Written by Eileen Daub

    About Eileen - I was one of those kids who said - "I want to be a marine biologist when I grow up!"....except then I actually became one. After a brief time at the United States Coast Guard Academy, I graduated from Coastal Carolina University in Myrtle Beach, South Carolina in 2004. Since then, I've been a marine biologist at That Fish Place - That Pet Place, along with a Fish Room supervisor, copywriter, livestock inventory controller, livestock mail-order supervisor and other duties here and there. I also spent eight seasons as a professional actress with the Pennsylvania Renaissance Faire and picking up other roles in shows around the area. I'm one of Those Crazy Hockey Fans as well (go Flyers and go Hershey Bears!).