GFO question

[WindeyD]

So I had a cyano outbreak several months ago which has been fixed and the tank looks great. Part of my fix was a BRS dual media reactor running carbon and GFO. After three months of running I changed mt GFO out last weekend and some of my corals (especially acans) don't look happy and are showing signs of stress. I used the exact same amount of GFO as was in there previously but think the new GFO has stressed the tank and have shut the reactor off. I know I should be monitoring my phosphates and a hanna checker is on my xmass list as I changed it out based on an arbitrary time frame. How do you folks advise I get my reactor back on line once my corals rebound? 'm Thinking about leaving it off until I get my checker to test levels, does anyone use GFO intermittently, say on a timer a few hours each day? Thanks for any advice!

 

[UK_Pete]

People say that once they change their GFO with new stuff, because its much more effective when new, it rips the phosphate down too quickly for corals. Rapidly plummeting phosphate levels have been blamed for coral bleaching and worse in many cases. If you let the old GFO get quite weak in its activity before you replace it, and you replace it with new stuff, your phosphates are going to fall quickly so its not advised. Personally I don't have enough corals to comment on this but I have read many threads on the same (you can search).

Shutting the reactor off is probably a good thing, and removing some of the GFO might be worth while. Whether the phosphates will naturally rise quick enough (or overshoot) to keep your corals happy is the question, and how much new GFO to leave in your reactor is another. Some people even dose phosphate but if you don't have a phosphate test kit and know what your levels were before you changed your GFO then you don't know what level to target. If you have the old media perhaps put it back in and wait for the tank to stabilise but you have probably chucked it out I guess. If you can put it back in you might be able to get someone else (LFS?) to check your phosphate so at least you know what your tank has acclimatised to.

I tried putting my GFO on a timer once but I noticed it became anerobic when switched off for a few hours (I smelt the rotten eggs) so IMO its not the way to go. Putting the GFO in gradually is probably the best way but without a checker its impossible to be sure about quantities.

Theres also anecdotes of phosphate being quite buffered in tanks, apparently (people are speculating) by adsorption on rocks etc, so with the GFO out of the circuit you would expect it to bounce back to fairly normal levels for your tank. Maybe some more experienced coral keepers can suggest a schedule to refill your reactor gradually thats worked for them. Immediate problem though would seem to be to restore stability to avoid any coral trauma and loss.

 

[Randy Holmes-Farley Verified Community Expert]

I think that if you are having troubles, then yes, measuring phosphate may be a good step to try to see why. For example, there may be different approaches if you dropped phosphate too fast, or too low. Or maybe it is neither of these.

Phosphate may have gotten pretty high during the months the GFO wasn't changed.

IMO, using less may be a better option than a timer.

 

[Randy Holmes-Farley Verified Community Expert]

Theres also anecdotes of phosphate being quite buffered in tanks, apparently (people are speculating) by adsorption on rocks etc, so with the GFO out of the circuit you would expect it to bounce back to fairly normal levels for your tank. Maybe some more experienced coral keepers can suggest a schedule to refill your reactor gradually thats worked for them. Immediate problem though would seem to be to restore stability to avoid any coral trauma and loss.

FWIW, I wouldn't call it an anecdote. It is well known in the scientific literature that phosphate binds to calcium carbonate from seawater at the phosphate levels we encounter.

 

[MattL22]

I run 2 two little fishes for phosban now and change 1 every 2-3 weeks alternating the one that I swap the Gfo a reef buddy of mine told me to add 1/2 ur amount then run it for week add next 1/2 to lessen the swing I liked his approach just tweaked it a bit using 2 reactors tank is a 220 with 60 gal fuge

 

[UK_Pete]

FWIW, I wouldn't call it an anecdote. It is well known in the scientific literature that phosphate binds to calcium carbonate from seawater at the phosphate levels we encounter.

Thanks Randy, didn't realise that. Does that mean that in a situation like the OPs, taking the media out will cause levels to fairly well stabilise back to the original level even without adding the original (used) media back? And I guess by extension theres even a bit of buffering against food additions etc while corals get over the shock of the original drop in phosphates. So maybe running GFO free for a week or so would be a good move?

 

[WindeyD]

Thanks for the help, I certainly believe it to be a sudden drop in phosphate that has stressed my corals, as all other parameters have remained stable and are well within what most consider good parameters: temp 79, Alk 8.1, Ca 475, Mag 1325, salinity 1.026, nitrate 0/undetectable,ph 8.3; the only thing that changed in my system was the GFO changeout and while a pre and post phosphate test would be nice to confirm that I feel pretty confident that that is the culprit. When I initially added the reactor with GFO 3 months ago my corals also showed signs of stress for about a week but then rebounded; actually many of them multiplied significantly during that time which I believe can be a response to stress. I guess what I've learned is 1. Testing my phosphate to determine exactly when to change out GFO, and 2. When changing out media it is likely best to slowly add smaller amounts of GFO over a period of time in order to avoid the sudden drop and associated coral stress response.

 

[Randy Holmes-Farley Verified Community Expert]

Thanks Randy, didn't realise that. Does that mean that in a situation like the OPs, taking the media out will cause levels to fairly well stabilise back to the original level even without adding the original (used) media back? And I guess by extension theres even a bit of buffering against food additions etc while corals get over the shock of the original drop in phosphates. So maybe running GFO free for a week or so would be a good move?

Without a reading, it is hard to know what is happening when using GFO which continuously binds more and more until it is depleted, but this effect is most clear when doing large water changes and not seeing the phosphate drop as much as would be calculated from the simple math of export, as would be accurate for something like nitrate.

 

[Randy Holmes-Farley Verified Community Expert]

I run 2 two little fishes for phosban now and change 1 every 2-3 weeks alternating the one that I swap the Gfo a reef buddy of mine told me to add 1/2 ur amount then run it for week add next 1/2 to lessen the swing I liked his approach just tweaked it a bit using 2 reactors tank is a 220 with 60 gal fuge

That is a fine way to soften the changes.