I can’t tell you how many times I come across fish keepers whose water parameters have suddenly degraded and they don’t know why. There are lots of things that can cause ammonia, nitrite, or nitrate spikes or even pH crashes and changes. However, there is one pretty simple solution to minimizing the probability of it happening – routine tank maintenance and consistency.
If you get in the habit of inconsistently performing regular maintenance tasks, you increase the chances that you will have a parameter crash or spike. When you clean your filters, do it the same way consistently. When you change your water, same thing. If you need to create a check list of some kind to keep track of what you have done, do so. In fact, it’s a great idea to keep a log of what you do to your tank(s). I log the maintenance of all of my tanks – filter cleanings, water changes, substrate cleanings, etc.
Crashes and spikes don’t happen randomly. There is a reason why they happen. Sometimes they’re caused by something unknown (e.g., an unknown dead fish). Sometimes they’re accidental (e.g., child dumps something in the tank). However, when a major parameter change does happen, ask yourself what you did just prior to discovering the change. And then think about that action and how it compares to your routine. Chances are high you did something differently – swapped out a filter, changed a greater percentage of water, added something to the tank (e.g., wood), changed the substrate, added a lot of fish or a few larger fish. If you did absolutely nothing different than you normally do, then look at things like missing fish, etc. There are multiple possibilities but 90% of the time detrimental water parameter changes are self-created.