Cloudy Aquarium Water Causes and Cures - The Spruce

You are facing a problem if your yellow water is due to dissolved organic carbons. This is a waste issue. You have a DOC problem if your water is cloudy, you have no aquarium wood in your tank, fish are sick or dying and there is an unpleasant odor. You may see clumps of decaying waste or dead plants. This problem is more common in brand new tanks and tanks in which you've recently switched to a new type of food. Improper filtration, infrequent water changes, dying plants, dead fish or invertebrates in the tank, overcrowding, leftover fish food and uncured gravel all contribute to DOC. Dissolved organic compounds can cause "toxic blooms," whereby microorganisms growing in the DOC deplete the oxygen in your tank and cause fish death.

I have 4 parrot fish, 2 blue arcua and 2 kissing guarumi. Tank and heater is second hand. Water is always cloudy and the heater goes way high

To answer your questions. Its kind of a milky white. Fish get a pinch of food in the morning and i crumble some tubifex worm cube in the evening for them. They eat all the food. Plus the plecostamus gets an algae tablet in the evening(which he devours). The fish have been getting this much food for as long as I had them. Had them in a 20 gallon for 2 years prior to getting the 30. Water changes are about 10%.
tank consists of 6 neon tetras, 2 black tetras, 2 dwarf gouramis and a plecostamus. My other 30 consists of similar fish and its crystal clear. Both tanks are in the same area of my house. Within about 5 feet of each other.
Water has been tested and everything looks fine. I tested it and also took a sample to two different fish supply stores hopeing someone could figure out the mystery. Water in cloudy tank srems to clear up after a water change, but the next day its cloudy again.

Over time, that cloudiness will resolve itself

Below is an awesome video from  that shows us actual time-lapse proof over a 5 period how a  eradicated the cloudy water in his fish tank. The most important thing is to be patient. You have to realize that an aquarium is a glass box full of living things, and no living thing is instant. Patience is sometimes difficult for us to achieve in this world where we can talk instantly to someone on the other side of the world, or call up a Web page in a billionth of a second. Fish, invertebrates and other aquatic life, including filter bacteria, require time to become adapted to their new home and begin to grow. If we try to rush the natural process of establishing a tank and immediately stuff a new tank full of life, things will go wrong.
When something like a bloom of cloudy water happens, first try to figure out what happened, and then, once you figure out what went wrong, correct it. Don’t just start adding chemicals and cleaning things. That might set the establishment of your bacterial colony back and actually prolong the period of cloudy water. Be patient.

Cloudy Aquarium Water - How to Fix Cloudy Fish Tank Water

Maintaining the filter is probably the most overlooked aquarium task. Filters are designed to support your tank’s inhabitants, and many manufacturers rightly call the filter a “life support system.” Follow the manufacturer’s instructions on maintaining your filter. You can have the most expensive, high-end life support system for your tank, but if you don’t keep it clean and in working order, it will fail. Even an old-fashioned, inexpensive box filter that is regularly maintained is better than the latest high-tech filter gadget that gets ignored.
Set up a regular schedule and maintain your filter. The slightest slowing of flow should be investigated and addressed immediately. Failure to do so could mean cloudy water or, worse, death for your fish.

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