I started my mixed reef tank almost three years ago. I started with dry Pukani, so In the beginning, I was terrified of a PO4 leeching so ran a GFO reactor with a refugium from the beginning. I had been out of reefing for about 5 years, and GFO was a new thing to me. I didn't realize it was stripping all the PO4, keeping leves at near/at zero. With NO3 levels in the 2-3 ppm range, the tank thrived for about 18 months. Then, through a stretch of stingy (lazy) feeding, my NO3 levels bottomed out. At that point I couldn't get PO4 or NO3 to measurable levels despite increased feeding and delayed water changes.
With PO4 and NO3 at immeasurable levels, I began a year long battle with cyano, then dinos that choked almost all my SPS and some LPS. I pulled the GFO, which led to some hair algae, which finally culminated in an infestation of Red Turf Algae I thought I could never beat (look for a post later on how I eradicated that with Brightwell Razor and MicroBacter Clean later).
Today, I run a small refugium with chaeto and a couple mangrove plants, good skimming, and 20% monthly water changes. I keep PO4 in the .01-.05 ppm range via the Hanna ULR through feeding regimen. If I do get a PO4 spike, which it does occasionally, I use Brightwell Phospat-E to get levels trending down between water changes.
When I started reefing 20 years ago, PO4 and NO3 couldn't be too low (maybe because testing wasn't as good?). Now, I am 99% certain that PO4 and NO3 bottoming out was the catalyst for my woes. I keep PO4 and NO3 additives around; I'll never let levels get to zero again, shooting for .01-.05 ppm PO4 and 3-5 ppm NO3.
