Hi Response and welcome to our freshwater beginners section!
All containers of dechlorinated freshwater will have the kind of cloudiness you are describing. It is caused by various microorganisms, both bacteria and algae (if there is enough light) making a new home. When we start a new tank we are setting up a new environment and these organisms will naturally begin their cycles. They are present all over the earth, so we don't have to introduce them artificially.
I suspect that what ZZ is working up to is finding out whether you've ever been introduced to the concept of "cycling" as tropical fish hobbyists call it. Its a shorthand term we all use for a set of processes that are key to keeping fish.
When fish move water through their gills to obtain oxygen and other needed substances, they simultaneously give off ammonia(NH3) which, in nature, is disbursed by millions of gallons of water. In our tanks, this ammonia joins up with ammonia from fish waste, excess feeding and plant debris. In fact, the way this other ammonia is created is by the action of heterotrophic bacteria that breaks the waste or debris down in to the simpler form of ammonia.
Ammonia, even in tiny amounts, is a deadly poison to our fish and in our small aquarium environments it can quickly concentrate to a level that stresses and then kills the fish. Ammonia stress can sometimes be seen when fish lose coloration and subdue their usual movement patterns.
There is an odd microorganism, a particular species of "autotrophic" bacterium which can process this ammonia and turn the leftovers in to nitrite(NO2), moving the nitrogen atom along a path we call the nitrogen cycle. Unfortunately, nitrite(NO2) is also a deadly poison to fish and even in tiny amounts it will begin to deprive the fish of cellular oxygen and lead to permanent damage or death.
There is yet another bacterium that can take this nitrite(NO2) and process it in to nitrate(NO3) which, while not a good thing for our tanks, is much better tolerated by our fish until such time as we can perform our usual weekly water change and remove this final nitrate(NO3) product from concentration.
Often, as a beginner, you simply hear someone say "oh, you need some good bacteria to build up in your tank," or some statement similar to that. Its really better to get a little more in to it and understand it in more detail because it is quite core to the hobby and eventually becomes a set of information that experienced hobbyists consider to be second nature.
In the hobbyist world we are quite careful and watchful about the process of starting tanks. This is quite different from the chaotic world of local fish shops making money and beginners trying to piece together whatever bit they've heard from someone. What we usually recommend for beginners is to go through a process of growing these two species of bacteria in their filter, a process we call Fishless Cycling. This typically takes anywhere from a month to two months or even a little more sometimes and results in a "working biofilter." A biofilter, that is, which can take all the ammonia and nitrite(NO2) in a tank and successfully process it at a rate to handle the load of fish in the tank.
In your case, one of the first things the members will probably need to know is the set of numbers from some good test results on your water. Its important to use a good set of liquid-reagent based test kits and many of us, as beginners, like and use the API Freshwater Master Test Kit or the Nutrafin Mini-Master Test Kit. Paper strips don't cut it.
Note that we have background reading for the things I've introduced here: The Nitrogen Cycle, The Fishless Cycle and The Fish-In Cycling Situation are all covered to some extent in articles in our Beginners Resource Center. You can read these and ask more questions as well as provide the members with more info about your tank and situation.
~~waterdrop~~
