I think you may have the wrong idea on tank maintanence, you should read up on treating/avoiding new tank syndrome as it will give you a better understanding on tank maintanence/your tank ecosystem

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http
/www.fishforums.net/index.php?showtopic=10099
In your filter sponge/media in your tank there resides beneficial bacteria that breaks down harmful toxins in the water to make them harmless, this beneficial bacteria needs 2 main things to survive;
a. A constant source of ammonia(i.e fish poop) to feed on and break down, and
b. A constant source of water flowing over it to supply it with oxygen to live and waste to break down.
Without your beneficial bacteria, ammonia(primarily created by fish poop) would build up and cause your fish to become sick and/or die. Certain things can kill off your beneficial bacteria, like cleaning out the filter sponge in undechlorinated tap water or taking too much water out of the tank at a time and starving your bacteria of ammonia.
Ph is not very important to know, the vast majority of fish can easily adjust to a ph that isn't exactly to their specifications, you should never mess/boost your ph, certain things can naturally alter it though like adding bodwood, sandstone, limestone, coral and vaiour other things.
The most important stats to know in your tank are ammonia, nitrites and nitrates as you will know if you read the link, in any tank ammonia and nitrites should be 0 and nitrates kept under 40 preferably- if any of these stats rise above their desired number you should do a water change imediatly. I strongly advise you buy your own test kits as many lfs's(local fish stores') will tell you your water quality is "fine" when actually it is on the brink of disaster.
Your basic tank maintance should be a 20-30% water change with dechlorinator a week plus clean the substrate, you shouldn't clean the filter sponge/media out more than once every 10days and if you need to do it, clean it out in old water from a water change and only remove the worst of the gunk/muck- if you over clean it you may kill off your beneficial bacteria. If you follow this basic tank maintanence, your tank will complete its cycle and mature into a healthy stress-free tank for your fish to live in.
Ammonia and nitrites in particular are very stressful for fish and often lethal for many, stress is a big issue for fish as when they feel stressed their imune systems don't work very efficiently and they are more prone to becoming sick. Many lfs's do not tell you this sort of info as they are just there to make sales, doing your own research is a vital part of fish keeping

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Does your fish appear not to be able to maintain balance in the water even though it appears it wants to?