Which points? These?
When a system is no longer able to properly support the animals, plants, etc that it is required to support and/or designed to support.
That's an OK definition, although it may not permit us to distinguish acute events, which many folks associate with crashes, from years long trends.
Do folks believe that an increase in nutrients (phosphorus, I presume) would necessarily lead to a crash?
Hello, this thing on?
So all folks with elevated phosphate must have already crashed, but missed the event while watching a commercial?
Are we just talking phosphorus, or do you include nitrogen, metals, etc,?
What types of aquaria are being discussed?
All of them
Including soft coral tanks, which I though you indicated might not be "crashed" by elevated phosphate and/or nitrate?
I still can't believe people are putting rust in their tanks.
What do you think it does that's bad?
Keeping in mind that using these "other mechanisms" you will only be removing the most reactive form of phosphorus, water soluble, limiting phosphorus - what has to happen in marine environments in order to have water soluble phosphorus?
I don't understand the question. All natural environments have water soluble phosphorus.
What would have to take place in a aquatic system in order to have something that's limiting available in it's most available, most reactive form?
Something else be limiting?
Nitrogen and iron can easily be limiting in natural and reef environments. So could other things, possibly, if these are all available. Or phosphate can be limiting. Or growth isn't nutrient limited at all, but rather by light/space/predation/etc.
I do not presume that phosphorus is limiting in all aquaria. You do seem to conclude that.