Cleaning your tank is an indispensable part of aquarium maintenance, but often the water in the tank looks markedly worse after cleaning is complete. When you clean your tank, you inevitably release dirt and debris that has been trapped in the gravel, and that can create a cloudy appearance in the water.
Those cloudy conditions are most likely to appear when you do your regular water changes. When you siphon water out of the tank, you loosen up the gravel and release the dirt that had been trapped there. When you pour the new water into the tank, you further disturb the gravel and set loose even more dirt and debris. You can reduce the amount of debris released into the water by placing a shallow bowl in the bottom of the tank and pouring the water into that instead. That reduces the agitation of the gravel, and thus the amount of debris that can cloud the water.
Even the most carefully maintained fish tank has a certain amount of trapped sediment, dirt and debris. This debris works its way into the gravel and, when the gravel is disturbed, it gets into the water and causes that distinctive cloudy appearance. Keeping the movement of the gravel to a minimum can reduce the cloudy appearance, but it is actually good to release some of that dirt and get it out of the water. Your normal filtration should take care of the cloudiness within a day or two. If you want to move the process along you can add a secondary filter temporarily, just until the water begins to clear up.
Siphon and Vacuum
You can clean your tank more thoroughly and reduce the cloudiness in the tank by using a combination siphon and gravel vacuum. Placing the gravel vacuum and siphon unit into the tank lets you suck out that deep-seated dirt and debris, while removing water from your tank at the same time. Since the debris travels straight through the siphon to your waiting bucket, it does not get into the tank and cause cloudiness. This gives you a more thorough cleaning, and reduces any additional housekeeping you need to do.
You can purchase a number of water clarification products at your local pet store. Some of these products are liquids that work by applying a set number of drops per gallon of water. Others are tablets that slowly dissolve and clear up the water. These products work by attracting the dust and dirt in the tank and having it form larger clumps that can then be carried away into the filter. If your aquarium does not have adequate filtration, these water clarification products will not work well. You might find it helpful to add an additional filter for a short time after each cleaning or water change. Combining the extra filtration with a commercial water clarification product is the fastest way to remove the cloudiness from your tank.