Is it time to change gfo?

cylon032 · Jun 25, 2021

Not sure if I should change it now or wait. Display tank phosphate is .18
Water coming out of reactor is .10
Do I wait till they match or does the water from the reactor always have to be at 0 or around a good range like .03?
Using Hanna ulr phosphate to test.

KrisReef · Jun 25, 2021

The media is still working and in theory it could take your tank to zero. I wait until I get an increase in tank reading before I change out media

Snoopy 67 · Jun 25, 2021

When the water out of the reactor comes within .03 to.04 it's time for a change.

cylon032 · Jun 25, 2021

Snoopy 67 said:
When the water out of the reactor comes within .03 to.04 it's time for a change.

So it should be zero when I change it then wait till it goes back up to .03 .04 and replace?

Snoopy 67 · Jun 26, 2021

NO-- never -0-
If water is .08 & reactor water is 0.11 - 0.12 change it.

Dkeller_nc · Jun 26, 2021

There's a good bit of debate about what the optimal inorganic orthophosphate level of an SPS tank should be. I won't wade into that particular debate (a search will yield dozens of hours of reading and/or argument). But if you're relatively new to SPS keeping, my only comment is that the consequences of phosphate levels that are above/below the oft-cited 100ppb level aren't symmetrical. The consequence of phosphate levels above 100ppb, even way above 100ppb, are generally excessive algae growth, especially in a new tank. The consequence of phosphate levels that are way below 100ppb are generally fading of SPS species, followed by rapid death of the coral (e.g., RTN). That's especially true for relatively new tanks that are less than a couple of years old.

Older tanks seem to be able to tolerate lower inorganic orthophosphate levels than "optimal", probably because such tanks would tend to have a much higher organic phosphate load. Most of us, however, don't test for dissolved and/or particulate organic phosphate because we don't do acidic/heated digestion of tank water samples to get a total phosphate, nor test the water samples before/after filtration to get an estimate of the dissolved vs. particulate phosphate.

Bottom line - I'd be extremely cautious about running GFO on any new tank unless you really have an out of control algae growth issue. And I'd be equally cautious about how much GFO you ran on such a tank, and would keep it to a bare minimum. The above, of course, is an opinion based on personal experience over the last few decades and, importantly, on a personal choice about risk to the coral versus the pain-in-the-tail factor of manual algae removal. It may help to know that I've kept SPS for about 30 years, and while I have GFO as a back-up in case all other control measures fail, I only very, very rarely run GFO on my tanks, and only then for a short-term period - perhaps two weeks, and intentionally use a low amount of GFO that I'm sure is not enough to take up the majority of the inorganic ortho phosphate in my tank water.