Tank size (l-w-d) 60cm-30cm-35cmThe...

Question
Tank size (l-w-d) 60cm-30cm-35cm
The tank has been set up for 5 months and is using a fluval 2 under water filter. The tank PH is 7 ammonia and nitrates are minimal.
The tank is stocked to slightly under the appropriate levels according to all the books i have read. There is an assortment of tetras, a single dwarf gourami, a clown loach and a syno eupterus catfish.
The problem i have is that about a two weeks ago a tetra died for no visible reason, before which the tank water was nice and clear. Since then the water has become increasingly cloudy. I have performed two small water changes, about 15% of the tank volume and each time the water has come out a cloudy green colour and within two days of the water change the tank has become deeply cloudy again.
Any suggestions on what the problem could be and how to solve it?

Answer
Hi Mark;

Cloudy or green water is a very difficult problem indeed. You will have to be very patient and keep trying different things if it doesn't clear up soon. If the water is milky-looking cloudy it is probably from overfeeding and/or from a filter change or tank cleaning. When the filter is changed it removes the beneficial bacteria that helps keep the system balanced. Excess dissolved waste shows up as cloudiness. This doesn't mean you should never clean the filter. You just don't want to replace all the media in it at once. Change part of it and wait two weeks to replace the rest. Or, rinse the media in a container of aquarium water and replace. This preserves the most important part of your filter, the bacteria that clings to the pads. Adding a second filter would help too. This way the system always has a good working biological balanced filter to keep the fish safe when one is changed.

Green cloudiness, also called "algae bloom" is from suspended algae particles or freshwater plankton. Green cloudy water is most common in tanks that are on the new side, less than a year old. Excess nutrients and carbon dioxide from overfeeding and/or overcrowding are the most common causes.

If the tank has any detectable amounts of ammonia or nitrite, there is something off balance in the biological system. Ammonia and nitrite should always be at 'zero' in an established tank. They are consumed by the beneficial bacteria colonies growing in your filter and on decorations and gravel. Nitrate (different from nitrite) is okay at 40 ppm or lower. It is removed only by partial water changes and is also consumed by live plants as fertilizer.  Excess toxins like ammonia and nitrite are also possible causes of cloudiness.

There are several ways to treat green water. Not all work for every tank though so you may have to try several. The first thing to try is cutting back on food and making 25% water changes twice a week or even three times a week for awhile. This will reduce the nutrients that feed the  plankton and/or algae. Also reduce the hours of light. Turn on the tank lights for only a few minutes every day to let the fish feed until the cloudy problem goes away. Feed them once a day and only enough food that the fish will finish it from all areas of the tank in 5 minutes. (This is the feeding rule all the time, and not just for the algae problem).

Be sure there is enough oxygen in the water by adding an airstone hooked to an air pump. All plants, including algae, put off carbon dioxide in the dark. Additional aeration will make up for that during the night. When the lights are on the plant life puts out oxygen so aeration isn't as necessary, but the extra oxygen sometimes helps clear green or cloudy water so it doesn't hurt to leave it going during the day too. Extra oxygen also helps benefical bacteria colonies to thrive. The tank is more balanced with more oxygen in the system.

Keep in mind the adult size of the fish you now have; Synodontis eupteris get 15 cm, Clown loach gets 30 cm, Dwarf Gourami gets 5 cm and most tetras are 2.5 to 3.75 cm. The maximum safe population for your size tank is 40 to 50 cm. You don't want to add any more to the tank because of the projected adult size of these guys.

Followups Welcome

At Your Service;
Chris Robbins

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