Can you please expand on the PH crash? I'm curious about this for future projects...
In a tank, over time, without water changes, you get "old tank syndrome".
Have a read of this:
http://www.algone.com/as-the-aquarium-ages-old-tank-syndrome-often-sets-in
Essentially, "The first sign of “old tank syndrome” is rising nitrate levels. The nitrification process, which oxidizes ammonia to nitrite and nitrite to nitrate, is continuous. The same process also produces hydrogen ions. Hydrogen ions directly influence the pH level. PH, in simple words, is the bonding of carbonate ions (buffer) with hydrogen ions. The more bonding, the higher the pH. Accumulating hydrogen ions will use up all available buffers. If none are left hydrogen ions will acidify the water, resulting in a steady but continuous decline of pH."
The less water, the more instable the parameters, so pH crash happens more rapidly.
This is magnified by my tap water already being extremely soft and slightly acidic, plus the driftwood in the tank. The hydrogen ions continually produced in a tank with bioload have very little to bond with due to minimal buffers in my water. Thus pH crash happens very quickly. I have a large bag of crushed marble in the filter to try to buffer a crash between water changes.
