Oscarfishlover.com

when i bought my 75 gallon tank, it came with two 12yr old balas, kind of big pleco,stripped raphfiel catfish, and a loach. and like 7 ugly goldfish that i gave to my friend for his outdoor pond...but neways the guy had conditioned all the fish for water that was straigt out of the tap!
lol i found it to be really wierd! has any one else heard of that?

I'm not sure that you can condition a fish to live in water that contains Chlorine / Chloramine without compromising its health. I would strongly advise you to use a water conditioner whenever you replace some of the water in the tank

i wasn't sure either...
but the guy had these fish living like this for six years, and when i got the tank the were doing just fine, and still are. and when i set up the tank i didn't put any water conditioner in it, and sure enough they did just fine...but before i put my oscar (achilies) in the tank i added the conditioner in.

His "Tap" water could be Well Water which does not contain Chlorine / Chloramine. I have been keeping fish of many different kinds for years in straight "Tap" water.

The reason you use tap water conditioner when adding tap water is cause it removes the chlorine in the tap water. Chlorine kills the bacteria in your filter and without these bacteria you end up with ammonia in your tank. Ammonia is poisonous to fish, more to some than others. Goldfish for example can live in ammonia, we all have heard and some of us kept goldfish in a bowl/tank without a filter. So obviously the fish you have have been able to live with some ammonia present. It not ideal and your fish will be healthier if you use a tap water conditioner

to add to what delboy said tap water conditioner also eliminates heavy metals which are present in well water.
also well water can contain higher level of nitrates than tap water which is monitored by the city.