Opaque water.

Question
Hi, I have two 20 gal. fish tanks. I've had them for about 2 years. One of them is just baby guppies and the other one that I am concerned of has 3 Plecos, 2 silver Mollies, about 5 guppies and 2 small pink catfish. Two of the Plecos and the catfish were added about 4 days ago. In it I also have two maternities for baby guppies and baby mollies. About a week ago I noticed that my water was foggy. I changed the filters, vacuumed the gravel, and changed about 25% of the water. This was yesterday night. Today I saw that the water was still the same. Today I changed the filters, vacuumed the gravel and changed about 10% of the water. I have two types of filters: One is an under-gravel and the other one is a normal filter. In order for my water to be crystal clear, do I have to remove the gravel and clean it? Because I think that I have overfed my fish. The level of the pH is 7.0, ammonia is normal and I don't know about my nitrate level. Can you please help me? Thank You.

Answer
Hi Marysol;

The cloudiness is from unprocessed fish waste. Beneficial bacteria lives in the filter that usually processes it, but it was removed when the filter was cleaned. This beneficial bacteria also lives in your gravel but your gravel may not have enough beneficial bacteria to process all the wastes by itself if it became too dirty. When you remove the filter media the beneficial bacteria is gone and has to re-grow it's colonies again. In the future, only rinse the filter media gently in a container of tank water to clear it. This gets rid of the waste but still preserves most of the beneficial bacteria colonies. Your filter media only needs to be replaced if it is literally falling apart from age or it can't be rinsed enough to allow the free flow of water anymore. I have some filter media that has been in use for literally years and all my tanks are always crystal clear.

If you remove your gravel at this point your system will have to start over as if it were a new tank. Toxins will then rise to lethal levels and you could lose your fish. Could be a total disaster. Yikes! Just keep doing 25% changes and gravel vacuuming every 3 or 4  of days until the system stabilizes again. Cut back on food a little for awhile too. Adding new fish added more waste and between that and filter cleaning, the beneficial bacteria that is left is just having a hard time keeping up. Just don't change more than 25% of the water in one day and it should get back to normal soon. The beneficial bacteria will grow where it needs to again and all should be well. Keep testing ammonia and nitrites to be sure they both are "zero" or are low and dropping. More frequent water changes will be needed if they don't drop. Do them every other day until the system stabilizes.

Once the system is back to normal, a weekly water change of 25% and gravel vacuuming weekly should be enough. Just don't overfeed and everything should be fine once again.

At Your Service;
Chris Robbins