lstorns, it's perfectly 'normal' for new fishkeepers who were given rotten advice to have many fish dying. New fishkeepers who are given proper advice need not have any fish deaths at all, unless through old age.
Liquid test kits themselves don't fix the problem, but they are the first step to knowing if there is a problem that the fishkeeper him/herself needs to fix.
Even well-maintained tanks - or tanks that the fishkeeper thinks is well-maintained - can developed issues with a spike in ammonia, etc.
"Perfection" in water levels isn't that hard to achieve, because unless one is dealing with very particular fish, or trying to breed certain kinds, "perfection" is 0 ammonia, 0 nitrite, and up to 20 nitrates; temp and pH can range and most fish, like humans, will adapt.
Prakash, thank you for continuing to listen to us just trying to help you have "happy, healthy fish" as achase put it!