[…] you are cleaning out your filters with tap water which kills your essential bacteria causing tempory bacteria bloom. or you are changing too much of the water causing bacteria loss.
Filters should be cleaned in old tank water, never under tap water, and the water does not contain a significant amount of bacteria, so water change size is not the issue from this point of view.
its recommened you do 10 to 20 percent water change each week. the more often you do water changes the better as large water changes can cause all sorts of problems and strewsse fish. the best technique i know is to change water daily. say for example i have a 260 litre tank. i change exactly 10 litres a day making that 70 litres a week. but seems as im taking out some recently added water each day it works out about 45 to 55 litres a week. i clean the gravel each time and this has proven to keep ammonia and nitrate at 0 and nitrate always below 20. thanks
It is recommended that one does not do large water changes irregularly because fast changes in water parameters are harmful to the fish and tank water has a tendency of drifting away from tap water. But there are also reasons for doing larger water changes: for example, to remove hormones that fish release from the water, which is why it is also recommended that fry tanks get large (50% or more), regular (daily or every other day) water changes instead of small ones as small ones would not help very much. This is also why a 10% water change will not help much with an ammonia reading, but a 50+% water change will help considerably more.
Daily, 10 litre water changes on a 260 litre tank are approximately the same as a 24% (62 litre) water change per week instead of one 27% water change, which is not too different; it's really with larger water changes that it makes a difference (for example, 7*50% water changes are similar to one 86% water change instead of 3.5 100% water changes).