why Prime? a little light reading for ya
if you'd like abit more information on the why's and why nots in dechlorination products.
all municipal water supplies must by law, be disinfected of bacterial and viral pathogens. until about 40 years ago, the principal disinfectant was chlorine. the problem with the chlorination process is that chlorine combines with natural organic matter to form potent, cancer causing compounds known as Trihalomethanes.
knowing that, most public and all municipal water systems have moved to the use of chloramine. this compound is produced as a result of the reaction between chlorine and ammonia. it has been common practice to use chloramine in the treatment of public water supplies for over 60 years but there are disadvantages to its use.
chloramine is a far weaker and slower acting disinfectant than chlorine and is especially weak for inactivating certain viruses. therefor, when chloramine is used as the principal disinfectant in your municipal water, ammonia is added at a point downstream in the process so that micro-organisms, including viruses, will be exposed to the free chlorine for a short period before the chloramine is formed.
all aquarium dechlorinators utilize Sodium Thiosulfate, which reacts with the chlorine (or the chlorine portion of the chloramine) to form harmless chloride ions. the chlorine is completely and totally removed and this reaction happens instantly. the tap water doesn't need to be mixed with the dechlorinator for any amount of time before adding it to the tank. It's perfectly safe to just add the dechlorinator as you add the water into the tank as many of you already do.
unfortunately, life is not always simple and there is one potential problem if your water is treated with chloramine. as i mentioned above, the dechlorinator reacts with the chlorine portion of the chloramine. the chlorine is thus eliminated, but the ammonia is left behind. if you use a simple dechlorinator that only contains sodium thiosulfate, you are solving one problem (chlorine) and creating a new problem (ammonia).
very few carbon filters can remove chloramine. the chlorine-ammonia bond prevents standard carbon from removing the chlorine. there are some new carbon filter units that are now using a special "Catalytic" Activated Carbon but as far as i know, this isn't available at your LFS. this catalytic carbon can break the chlorine-ammonia bond, and absorb the chlorine.
there are tap-water filters that add a special ammonia absorbing compound (zeolite) in addition to the carbon but zeolite has a fairly small ammonia absorbing capacity and needs frequent replacement.
so what should aquarists with chloramine in their water do about it? ALL chemicals sold for use with chloramines break the chlorine-ammonia bond. many of these dechlorinator water conditioners additionally include chemicals to convert the toxic ammonia into harmless ammonium. some of these are Seachem Prime, Tetra "AquaSafe NH/CL Formula", Jungle's "ACE", Kordon's "AmQuel", and Kent's "Professional Ammonia Detox".
If the label doesn't specifically mention that it neutralizes ammonia, then you must depend on your biofilter to do the job. generally, that shouldn't be a problem but it 'can' create a temporary ammonia spike until the bacteria act on it. thus, Seachem 'Prime' and similar products are safest.
