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This is a common mistake You added too many fish way too soon. the trick with fish is letting the tank cycle (allowing the positive bacteria to create a bio filter) This takes time. Then you add two fish once a week until you have your tank stocked However since you already have the fish. There is a product you can buy at petsmart called CYCLE add this since you already have the fish in place. Do partial water changes OFTEN 25% every other day as you have an ammonia spike and in order to keep the fish alive you must lower the ammonia the combination of the CYCLE and water changes will help however your tank will not be "clear" until the bio filter has become well established and balanced so be patient. Once the tank is balance or "cycled" you can drop down to weekly water changes. You do not want to vacuum the gravel too excessively until the tank has cycled as doing so will remove the positive bacteria. Hope this helps

I also think your tank is cycling I just started a 20 gallon 4 weeks ago and did the same thing. Had way to many fish in there to start the tank right, about 8 altogether. All my fish got sick from the cycling and had to start over. This time I went and got a 6 zebra danios because they are very hardy. Then I found someone willing to give up a couple cups of gravel from their tank. Just make extra sure their tank is healthy and well established. Add that (and no more gravel yet, its easier to cycle with just a tiny amount of gravel you can add more after cycling is done and the process is established) and try to find a "Wonder Shell" at the pet store. My tank stayed clear and 2 weeks later I added 4 guppies. 2 weeks later I tested and my tank was finally cycled. I was able to then add 5 cory cats and now my tank is full and healthy. Just takes time and patience. Change out 20% of the water twice a week, use the water conditioner and DONT vacuum the gravel often the first month as bacteria from the old aquarium will be multiplying and you don't want to destroy that process or your tank wont cycle properly. Also don't clean off the round floss wheel in your filter right away, just change the carbon filter once a month. They grow well on that wheel also.

New tanks need to cycle. Unfortunately you put too much in there at once to get things started. There is not enough of the bacteria that breaks down the waste present yet.

You can speed up this process slightly with a bacteria supplement such as Hagen Cycle or API StressZyme, but it will still take 4-6 weeks and most likely you will lose some fish.

To give the fish some relief, to a small water change with a gravel vac every 3-4 days, about 10% or 1 gallon.

The pleco will soon grow larger than the tank itself, be prepared to get rid of it or get a MUCH bigger tank.

http://fins.actwin.com/mirror/begin-cycling.html

What you have is often called a bacterial bloom. The problem is you did a lot in one day. As part of you filtering systems, there are bacteria that help break down the waste that you fish produce. Often in a new tank such as yours, when too many fish are added at one time very early on, it can cause this "bloom" in the bacteria. There is so much food in the water for them that they multiply like wild fire! Do a water change at least 15-50% at least once a week and you will see that as the tank starts to stabilize the bacteria will decrease in numbers and the cloud will disappear. Just be patient it may take up to 3 weeks for it to look like your fish are swimming through air.

You may be overfeeding.

Change no more than 50% of the water. This is because of the beneficial bacteria growing that you want to save. It will clear up like a miracle- dechlorinate that water first though!

It's better to underfeed than to overfeed. That old food sitting around decays really fast and makes it nasty and toxic in there.

Like he said it could just be cycling, and will eventually settle, but it also helps to get little sucker fish for youor tank. They'll just clean and eat all the algea off the walls of the tank. That way you won't have to keep cleaning all the junk out of the water, and scrub the sides of your tank.

You are not doing anything wrong. The tank is cycling. This is common with new setups. Check this site out.

hi change the water and start over. hint distilled water is better then tap water.