Do you have a good liquid-reagent based test kit? Many of us like and use the API Freshwater Master Test Kit. Results from these tests would be a starting point for the members to be able to give you meaningful help. Good water change technique involves, typically, two basic concerns. First, for less risk, you should dose the return water with a good conditioner (Seachem Prime is one of the best examples) at about 1.5x to 2x the amount instructed on the bottle so that chlorine or chloramine is removed from the tap water and various other concerns such as excess heavy metals or trace ammonia can be handled better. Secondly, its good to roughly temperature match the return water. Using your hand to judge a matching temperature is good enough for getting this within a couple degrees. A third, more rare, concern happens when a tank has not been maintained properly over time. Normally, the routine is to change some percentage of the tank water each week to guard against the buildup of trace metals and various organics. If this is not done over a period of months or years then the fish can grow gradually used to abnormally high levels of these things and be badly shocked if a large fraction of the water is suddenly changed.
~~waterdrop~~
