I bought a 75 gallon filter for my 55 gallon tank thinking it would do a lot better then what I had in there, but its been 2 days and the water is a little cloudy. Its not bad at all but it wasn't like this before. Does the biological filter need time to grow the bacteria and should I put the old filter next to the new one until its set up?

Did you by any chance turn the old filter off when you put the new filter on the tank?

Yea

Opps. If it makes you feel any better, I did exactly the same thing a few years ago when I first got into fish keeping. Next morning, tank was cloudy and stinking to high heaven.

What you've got to do is try and get an understanding of how your biological filtration works. Inside your filter you have all your media. A lot of filters have biological filtration which often come in the form of little balls. They also have sponge filtration, this is often what we refer to as mechanical filtration. They may also have some kind of carbon filtration which is usually black. Your biological filtration is where you bacteria live and thrive, this is what deals with ammonia and nitrite. Ammonia is what is produced from your fish when it goes to the toilet, or breathes. It is also produced from decaying matter such as food and plants. Your mechanical filtration is what catches all your waist. This type of filtration can be changed on a regular basis if you want. However, your biological filtration must be cared for very carefully. The bacteria that live in the biological filtration need oxygen to survive. They get this oxygen from water running through the media. As soon as you turn the filters off, the water stops flowing, and the bacteria are starved of oxygen. After four hours, they will all die.

This is what happened with you. So unfortunately, you are going to have to cycle your tank all over again. The reason you have cloudy water is bacteria is building up in the water to deal with the ammonia. These are free swimming bacteria are not the same sort that are found in your filtration. So what you then have to do is a water change every other day and test your water for ammonia, nitrite and eventually nitrate.

When you have established a healthy biological filter, you must never turn it off for too long. You must clean it very carefully and always in existing tank water, never under tap water.

So there you go, you won't make the same mistake again:laugh:

This is a common mistake. You think the filter on your tank is like other filters (like the oil filter on your car) and you switch it on and it starts working. As OFL says this isnt the case with filters for fish. I thought exactly the same as you until someone kindly explained it all to me. I now treat my filters with as much care as my fish

As your tank is cycling i would do 50% water changes everyday. Test your water regularly for ammonia, nitrite and nitrate. Once the result for ammonia AND nitrite are zero then go back to your normal water changes. I would suggest 50% once a week, and test your water every month, ammonia and nitrite should always be zero and try to keep nitrate preferable below 20 but below 40 is acceptable. If nitrate is too high then either do more water changes or feed the fish less.

The best thing i ever did was buy testers (the liquid ones are the best)

I bought some StressZyme just to see if it helps then after work did water tests. Amonia and Nitrite 0 Nitrate was between 15-20. The tank is clearing up so hopefully this is the end of it. Thanks for the advice, I won't make that mistake again.

Dont forget test regularly at least once a month, once everything is running ok. It the best way to give you an early warning if your water quality isnt good enough and then you can put it right before your oscar gets problems. If things are not right and you dont test you will only find out when you oscars health suffers