OK. I'll take up the buffering bit.
In simple terms ... The water you first put in your tank contains minerals, one of which is HCO3
- (bicarbonate), which happens to be the main buffer in FW
system. H+ (hydrogen ions = acid) reacts with the HCO3
- to make CO2
(which escapes the tank). As long as you have HCO3
- in your tank, it will eat up any H+ produced, and your pH won't change (much). BTW
, when there is a shortage of H+, the buffer system can also gives off H+, so your pH won't rise much either.
The problem is that as H+ is produced, the HCO3
- gets used up. When it is all gone, you have no buffer left, and any H+ produced will remain, thus your pH drops or crashes ... bad for fish.
Where did the H+ came from? The fish. Fish produces ammonia (NH3
). When the NH3
is converted to NO2
, H+ is released. Plus, fish also produce various organic acids as waste.
That is one more reason to do regualar partial water changes, to replenish your buffers, and to get rid of other wastes.