P has been an problem for me on the dentist's office tank for well over a year, I never had zero P, but never had a problem. Srusso's tank had huge P problems with a great growing scrubber and bryopsis going wild until he killed the P with GFO. Many others have commented on P issues. So maybe most tanks went to zero/zero but not all tanks, and like I said the most common long term problem/issue that I have seen mentioned, repeatedly, has been N=0 and stalled P absorption.