Fresh water tank crash

[asylumdown]

So you think it's likely an oxygen thing? The tank hasn't had any major changes in it for about 7 months so it was just so shocking to have this happen now. Other than an airstone is there anything that can be done to prevent it from happening again? Every so often I try and take out most of the plants so I can properly clean the gravel, is this something I need to worry about every time I do that (I know way more about salt water systems I'm afraid)?