YT, I learn abt this low po4 bleach thing from mike pallette video (its one of the video posted lately in my thread). He mentioned po4 is the energy building blocks for corals. If po4 is too low(<0.01) or zero, growth will slow down and eventually starts to bleach. Which kind of make perfect sense to me as I also notice the sps seems happier with a little po4 then no po4. The colours are deeper too.
Ps: tofu, sorry for invading your thread
Cheers,
James