What happens when GFO is exhausted?

[CoralReefer1019]

I run gfo in my system but what happens when it’s exhausted does it go back into the water before I can change it out?

 

[saltyfilmfolks]

It’s absorbtion (bonding actually) is maxed therefore the ions being bound. Just pass by.
I don’t belive it acts like aragonite and falls back into equilibrium with the water. Ie leaching.

 

[pdxmonkeyboy]

...an angel gets its wings.

what happens is nothing. the phosphate is bound to the gfo, it isnt going to leach unless something acts upon it.

 

[CoralReefer1019]

...an angel gets its wings.

what happens is nothing. the phosphate is bound to the gfo, it isnt going to leach unless something acts upon it.

What would act upon it? I usually change mine out once a month and use standard BRS gfo

 

[JDtimk]

I realize you are talking about whether or not GFO leaches back into the water after it is exhausted. But another aspect of the effect of GFO being exhausted that I worry could be harmful, is that there seems to be a relatively rapid rise and fall of the available po4 in the water column when GFO is used.
I am thinking of this scenario where let's say there is .1 ppm of po4 available in the water column before the GFO is employed. Then while the GFO strips out the po4 the total available po4 in the water column goes down to maybe .05 or lower, but when the GFO is exhausted the po4 in the water column goes back up to .1 or so ppm.
I think this rapid rise and fall can happen pretty quickly if there is enough GFO used, with enough flow through the GFO canister and if there is a constant source of po4 that is contributing to the po4 level in the water column, like detritus compacted into the sandbed or po4 leaching out of the argonite or constant over feeding.
I think the obvious misuse of GFO use is stripping the water of all po4 and we think of that as the thing that can cause an issue with GFO use, but I think that rapid rise and fall cycle of GFO use can also cause harm to coral.

 

[madweazl]

I've been using GFO for a little over a month. Within the first three hours of use, phosphates dropped from .23ppm to .12ppm. Over the course of the following few days, I dialed it in to provide a consistent level of removal and it's been hovering around .1ppm since (with a low of .05 over the course of a week). There were no observable negative impacts to our corals (little more polyp extension however). The reactor runs for about three hours a day now (comes on 16 times a day for about 11 minutes each time). I plan to dial it in a bit more to get to around .05ppm.

To address the original question, the first round of GFO lasted eight days before being exhausted (1/4 recommended dose). Once exhausted, the phosphate levels climbed back up to previous levels within a day or two (25 Jan in the log). Round two has lasted almost a month now.