I think that even if you don't introduce it, it's gonna get introduced anyway. I think that we already have P in our systems from the get-go. If you could find a salt mix that was 100% Phosphate free, and verified that your RO/DI water was absolutely Phosphate free and put this salt mixture into your tank it wouldn't take very long at all for an airborne bacterium containing organic Phosphate to land in it. This bacterium would eventually die so we would now have our first instance of inorganic Phosphate as well.
I have always liked the following slideshow. It's not geared for reeftanks but it shows things on a global scale. It also describes briefly the different forms of P like Boomer and Mike were discussing. If you read carefully, it also discusses how Ammonium can keep recycling as well. (For those who want to read every slide, it also describes why Iron-based Phosphate removers are efficient).
Slideshow on Marine Nutrients
I looked at my original post and I want to define a word I used. I know I'm describing this wrong but this is how I think of it. I used the word "limiting". The first time I saw this word on the boards, I was
. I simply didn't know what it meant. To me the word limiting means "if ya don't have it, you're gonna die because it is a requirement to keep living".
The attached pic is also not reef tank related by I like all the pretty circles.....just kidding.
I'll see if I can find a decent reef-related link about this.
Obviously, being careful about the input is important for Phosphate maintenance. We can also use macroalgaes and skimming for removal. We especially want to get rid of detritus before it breaks down and this can be accomplished in numerous ways.