Yes, correct answer on media replacement by Hungrydoug.
Hi Marzi and Welcome to TFF!
You have a RARE opportunity. The vast majority of our newcomers find us after the LFS (local fish shop) has already convinced them they only need to "wait a week and get fish!" They search and find us after serious problems are already starting and often their fish are dying. In your case you've found this hobby site before ever even putting water in, so if you choose to and have the patience, you could really learn to do it the right way. This is a very unusual site with a really large number of very experienced fishkeepers and a lot of great members who really share a lot of info with each other. It even has "scribes" like my who yak and lot and hopefully get people together
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Anyway, Hungrydoug is exactly right, there's no way you'd ever stumble into the hobby imagining that growing bacteria in the filter media was probably the single most important core thing to be learning first. But that's what our beginner forum is all about, sharing that kind of arcane stuff. Very often the single most important learning purchase for beginners is a good liquid-reagent test kit. Many of us like and use the API Freshwater Master Test Kit, or there are other decent liquid kits out there. HD has pointed you to our reference article by rdd1952 on the process of the Fishless Cycle and that's an important one to read. Your other homework in the "Beginners Resource Center" is to also read the Fish-In Cycling Situation and all about the Nitrogen Cycle and tank setup. These will generate more questions you can ask here in your thread.
OK, let me pause a moment to answer your question: in general almost any "water conditioner" will do a good job these days of removing the chlorine or chloramines that the water authority puts in the tap water. That's because they all use basically the same chemical to do it. But it turns out that "conditioner" is a popular product to put extra "features" in and these extra features and how well they are done vary quite a lot with different products. In my opinion Seachem Prime is the best of these, partly because it is as concentrated or almost as concentrated as the pond dechlor products and partly because it has the best reputation for doing a great job of detoxifying ammonia into ammonium and of binding up trace heavy metals such that they are less harmful. Prime is just a great product for beginners to use for at least the first year or two. After that when the tank is much more stable, they can switch to a cheaper pond product if they want to.
Let's go back to the bacteria thing: You'd never imagine that the filter they sell you is really just a "hardware kit" and needs to have a bunch of work done to it (work that you only know how to do from either being a hobbyist for years or from a site like this.) Filters perform 3 types of filtration, mechanical, chemical and biological. Most media types are especially good at one of these functions but will overlap and also perhaps perform one or more of the other functions also. When most people think of filters they're just thinking of the "mechanical" function, catching particles of debris. The "biological" function though is the real magic. That's the one that carries out the "Nitrogen Cycle" you're going to read about. Learn that as a beginner and you've learned perhaps the most important core thing of the hobby. The "chemical" function is special. Its optional and temporary and carries out special tasks from time to time.
When fish move water across their gills to get Oxygen, the gills also give off CO2 (just like humans) but also NH3 (ammonia, not like humans at all!) The amount they give off is significant. Fish waste, excess fish food and live plant debris also break down in our tanks to form even more ammonia. Ammonia, even in tiny amounts, causes gill damage, leading to shortened fish lives or death. In nature, ammonia is carried away from the gills by millions of gallons of fresh water. A box of water, even with a pump moving it, is nowhere near a match for that.
Luckily for fish hobbyists, it was discovered early on that bacteria could be grown in a filter to process this ammonia. What we now know is that a specific species of bacteria (Nitrosomonas spp. and perhaps similar strains) is the one that processes ammonia(NH3) into nitrite(NO2). Unfortunately, nitrite(NO2), is also quite deadly to fish: Even in tiny amounts, nitrite(NO2) attaches its two oxygen atoms (just like real O2 from air does) to the hemoglobin protein that's on fish red blood cells. Nitrite then proceeds to cause a reaction that changes hemoglobin into methemoglobin, which can't carry oxygen. This of course suffocates the fish, with nerve and brain damage being the most sensitive and first reaction. So, like ammonia, nitrite(NO2) causes shortened fish life and often death.
Once again, luckily, a second specific species (Nitrospira spp. and probably similar strains) comes to the rescue and grows along with the first species and processes the nitrite(NO2) into nitrate(NO3.) Nitrate(NO3) is much less harmful to fish and can be easily removed by our weekly water changes, prior to it having a negative effect on the aquarium.
All of this is known as the "biofilter!" A tank where a working biofilter has been "grown" prior to introducing any fish, is a tank that will provide a near perfect environment for those fish to begin to adjust to. The process of growing a biofilter is known as "cycling" which comes from the "Nitrogen Cycle" of environmental science, which describes the overall process that this all fits in to.
Since 1980, fishless cycling with simple household ammonia used as a way to drive the growth of the 2 correct bacterial species has grown and grown in the hobby. Using simple ammonia allows tighter control over the gowth process and produces the safe environment that serves as a jumping off point for the entire aquarium ecosystem shortly after fish are introduced.
~~waterdrop~~
