GFO time to change

[Fish Keeper82]

I had high Phosphates 1.41ppm when I cycled my tank.
after adding GFO and a water change they went down to .56 in 3 days( attached chart) well looking at the chart, looks like its time to change the GFO since its not going down much in the last couple of days. Would you agree? or should I wait and test again?

[ryeguyy84]

I'd say replace it. at that level you'll go through GFO pretty quickly.

[shermanator]

GFO works quick (especially at very high phosphate), so yes, it's probably at max capacity.

That said, if your high phosphate is from leaching rock, you are going to spend a fortune in GFO to get PO4 in check. You'll also see a rebound in the amount of phosphate in the water column after you remove the GFO (or do a water change). Do you have livestock in the tank?

[Fish Keeper82]

Yes i have a blue tang and green chromis. Yes the rock and sand I'm sure are leaching phosphate.this should not be for long because this rock was dead rock but it is from my old tank that sprung a leak. So basically this 160lbs of live rock was what i used as ammonia source to cycle my tank.
I'm just a noob with regards to GFO and didn't know how fast it reaches capacity. I hope after this next GFO change ill be at low levels. Thanks will change soon

[bertoni]

I agree that GFO works quickly. With the level that high, I'd guess that the media is shot within a few hours, depending on the flow rate. You can keep up with the GFO, but there are cheaper alternatives if cost becomes an issue. Also, GFO can be regenerated if you don't mind working with toxic chemicals.

[Fish Keeper82]

is there any problem with rinsing GFO with tap water prior to placing in reactor as opposed to discarding the first gallon of saltwater?

[bertoni]

I rinsed mine with tapwater and it seemed to be okay, but my tanks didn't have much of a phosphate problem in the first place. The tap water would have to be amazingly high in phosphate for a brief rinse to make a difference.

[Fish Keeper82]

I did a rinse with RO/DI just to make sure there are no "x factors" in my initial GFO experience. After parameters are good I believe I will rinse with the tap.
Thanks all for the input.
I'll post my PPM tomorrow cant wait to see how much it goes down with fresh GFO.

[ryeguyy84]

I dump a gallon of saltwater into the tank and then remove the first gallon. It's like a mini water change.

[Aquamechanic]

I ran 1000gm Rowaphos in a 600 gallon system that had PO4 topping the Salifert test out at 3ppm. After a week I was getting a reading just below 3. It took a month to get down to .25 - .5 and then stabilized. After nearly 2 months it began to rise again (probably leaching out of rock/sand )so I changed it out. After a week it has dropped again to .25ppm.

In my case the absorption rate and maximum capacity seems to have taken a while to reach. I am flowing water over the bag of GFO in the sump but disturb the bag every few days to avoid caking. I suspect a tumbling reactor would make it a quicker and more efficient process. GFO will clump if not disturbed and becomes less efficient.

If you suspect the media has reached capacity, take a sample of your water and test PO4. Put the suspect media in a gallon of tank water in a clean pail and lightly agitate with small powerhead to keep water moving. Test water in pail after 24 hours and see if you get a reduced reading.

I want to get maximum use from this stuff given the cost. It does work well though.

[Fish Keeper82]

I got some interesting results. Hanna checker read .31 with fresh GFO after two days. I'll have to recheck in a bit since this don't seem right considering the trend. the only thing I did different was pre rinse with ro/di and very little like half gallon.

[Fish Keeper82]

after retesting I got a reading of .25 ppm with a +/- .04 accuracy the .31 was not off by much . so my question is with this lower ppm than my original1.41 will the GFO take longer to remove Phosphate at this "lower" level?

[bertoni]

I'd still expect the GFO to be shot within a few hours with the phosphate at 0.31 ppm.

[Dan_P]

I had high Phosphates 1.41ppm when I cycled my tank.
after adding GFO and a water change they went down to .56 in 3 days( attached chart) well looking at the chart, looks like its time to change the GFO since its not going down much in the last couple of days. Would you agree? or should I wait and test again?

Nice data!

Yeah, time to change when the concentration levels off.

[Fish Keeper82]

I'd still expect the GFO to be shot within a few hours with the phosphate at 0.31 ppm.

WOW really??? My data didn't support that. With the first addition of GFO as you can see from the chart. Data showed lowered phosphate up till day 7 with start of phosphates at 1.11
Days with the red diamond is when I used fresh GFO

[bertoni]

That's interesting. Other people's data have shown that the media dies fairly quickly. How much media is in the reactor? How big is the tank? Is the media tumbling a bit?

[Fish Keeper82]

110 gallon system (125gal tank, 20gal sump minus the rock and sand =110)

1.75 cups GFO the first time(regular not high cap), I used 1.50 cups the second time (BRS single reactor)

Yes media is tumbling.The first time I was tumbling much more than this second time after finding a video on BRS showing correct tumble rate.

[bertoni]

Hmm, well, that does seem like a lot of media. Maybe that's the difference. I think I'll be careful to mention testing the phosphate level of the output before ditching media.

[Dan_P]

110 gallon system (125gal tank, 20gal sump minus the rock and sand =110)

1.75 cups GFO the first time(regular not high cap), I used 1.50 cups the second time (BRS single reactor)

Yes media is tumbling.The first time I was tumbling much more than this second time after finding a video on BRS showing correct tumble rate.

Holy smokes, that is a freakin boat load of GFO.

Rowaphos is suppose to adsorb 25 g of phosphate per kg of GFO. 110 gallons of water with a phosphate level of 2 ppm is 0.8 g of phosphate. Only 32 g is required. Even with the questions of capacity and volume v weight of GFO, something strange seems to going on.

I suppose you could invoke "my live rock is leaching phosphates" arguement. I would think this might double or triple the amount of GFO needed, getting it somewhat closer to the amount you are using. What do you think?

[shermanator]

GFO does have a very fast rate for absorbing phosphate. However, if your rock and sand have high amounts of phosphate bound (you said they did in post 4), you'll be observing the equilibrium of calcium-phosphate <-> phosphate in solution. Remember that when ever looking at kinetics of a system, you always observe the slowest rate constant.

[Fish Keeper82]

I didnt know this was a lot of GFO. Using the BRS calculator for 110 gallon of water i belive it came to 1.72 cups GFO. This was all i based on amount of media.... regardless ill let it do its thing for a couple of days and I'll post results.

[bertoni]

However, if your rock and sand have high amounts of phosphate bound (you said they did in post 4), you'll be observing the equilibrium of calcium-phosphate <-> phosphate in solution.
Right, I forgot about the time required for the phosphate to move from the rock to the water column. Sigh! I think we don't see this issue as much because most people don't add that much GFO at a time. It seems to work well, though.

[Fish Keeper82]

.21 today still dropping slowly. I'l check again in a couple of days. Now I'm wondering if I changed the first batch prematurely.

[bertoni]

Could be. That's a lot of GFO.

[Fish Keeper82]

Could be. That's a lot of GFO.

How much GFO should i use?. I'm going straight off the BRS calculator. not really trying to make an experiment with higher amounts.

[tmz]

I just check the effluent from the gfo reactor for PO4 and compare it to the reading for the aquarium water when I think the gfo is depleted.

Live rock exposed to high levels of phosphate will likely have some PO4 species bound to it's surface which will leach back into the water as the level in the water declines. This can take months . Removing the rock and treating it in a curing bin with water kept low in PO4 with lanthanum chloride is a faster less expensive option for rocks that can be easily removed from the aquarium.

Using large amounts of gfo when the PO4 is very high may be ok, albeit expensive. However ,as the PO4 goes down to the .1ppm range or so using too much gfo could cause a rapid fall or phosphorus deficiency which can upset corals , clams and othe5r organisms.

[Fish Keeper82]

Just an update

Phosphate levels finally getting in low range .04 ( with a .04 margin of error on hanna checker):dance:

Now that phosphate is at better level how much GFO should I use? Everyone seemed to be surprised when I posted 1.72 cups of GFO for 110 gallons as suggested by BRS calculator.
I realize too much GFO can hurt corals(don't have any yet but will begetting some soon).
What amount would you suggest I try?

[bertoni]

How are the animals in the tank doing now?

[Fish Keeper82]

All in tank is a blue tang and green chromis doing great. And a bunch of cerith snails

[bertoni]

Hmm, I might ramp down the GFO slowly, and watch the phosphate level. I might take out 25% at a time, and go for a week or two to see how the tank responds. There's going to be a lot of guessing along the way because we don't have any useful way to determine how saturated the media is with phosphate, but that is the usual situation with reef tanks.

[Dan_P]

All in tank is a blue tang and green chromis doing great. And a bunch of cerith snails

I appreciate your data plot. You would expect this trend when you adsorb PO4 from the water and then adsorb what leaches from the substrate and rocks: quick drop followed by a slow decline. Nice demonstration.

Your next step depends on the question you want to answer. One question could be "is there still a lot of PO4 bound to my substrate and rocks". You could answer this by removing all the GFO. If exposed surfaces are still saturated, the PO4 will rise over night. If the PO4 is bound deep in side the rock or substrate, the PO4 level will rise more slowly. Unless, you are really overfeeding, PO4 from food won't be a confounding contribution.

If you have a goal to maintain a very low PO4, continue to use GFO. How much? You have choices. Follow the manufacturer's advice. Or knowing that GFO has a capacity of 25 g PO4 per kilogram of GFO, calculate how much you need to adsorb the total amount of PO4 currently in your system. Or use the online calculator if you trust it.

When do you change the GFO? I saw advice about monitoring the output level of the GFO reactor. You could also look for a rise in the PO4 level in your system to indicate exhausted GFO. If the PO4 level in the system is below the detection limit, you won't detect the rise until your system level has a sufficiently high level to detect it. If this is too much for you, change out the GFO on a regular basis even if PO4 is not detected.

[Fish Keeper82]

Hmm, I might ramp down the GFO slowly, and watch the phosphate level. I might take out 25% at a time, and go for a week or two to see how the tank responds. There's going to be a lot of guessing along the way because we don't have any useful way to determine how saturated the media is with phosphate, but that is the usual situation with reef tanks.

Thanks all for the advice.:bounce1: As you can see from the chart attached I have not changed my GFO since the 27th of May and my phosphate is not going up from leaching rocks and tank looks great, so I do not expect to change the GFO for another month or so and when I do ill probably drop as per you suggestion Bertoni if not maybe a bit more.
Thanks again all:bounce1:

[bertoni]

You're welcome. Good luck!