High phosphate levels are a
recipe for disaster in saltwater aquariums. It is a nutrient for
nuisance algae and also hampers the formation of calcium skeleton in
corals. There are several different methods for dealing
with phosphate levels but one they I like is using granulated ferric
oxide (or GFO) in a media reactor. GFO is best used with a media reactor
for several reasons.
First, it is a very fine media and would easily escape from any bag you put it in.
Second, it clumps together if you don't have water moving through it.
When using GFO in a media
reactor watch the flow rate of the water through the media. It does not
need to be very fast at all. You don't want it looking like boiling
water where it is throwing up small particles in the
reactor. You just want the very top inch or less turning over ever so
slightly like water right before a boil. Otherwise you will get GFO dust
all inside your sump and possibly inside your display tank. Depending
which reactor you choose, it is a good idea
to run the output of the reactor into a filter sock. Worst case
scenario some GFO fines get into the filter sock but this way you can
avoid the disaster of GFO fines everywhere.
(Mr. Saltwater tank recommends the SpectraPure Dual Media Reactor (https://www.saltwateraquarium.com/mr-dual-independently-controlled-dual-chamber-media-reactor-spectrapure/
where you can adjust the flow rate through each chamber of the reactor.)
While some people test
phosphate levels frequently to know when to change their GFO but I just
replace it on my clients' systems at regular intervals. It is just
easier that way .
I recommend using GFO from the
very beginning of your system so any new corals you put into the system
will never get used to elevated levels of phosphate to begin with.
Elevated levels of phosphate will usually cause
them to brown out because the symbiotic algae inside them
If you already have a phosphate
issue and are introducing GFO to a well established reef, start off
with a small amount and proceed slowly. Though high phosphate levels
aren't good, many corals will not be happy and
may even end up dying if you pull the levels down too much, too
I use and recommend GFO and if
your tank already has a high phosphate issue (> 0.10 ppm), start with
a little GFO and add more to slowly bring down your phosphates.