GFO already spent?

[DrBoxedWine]

I added a gfo reactor to my 75g about 2.5 weeks ago, I was having a big algae outbreak and it did help. I'm noticing I have to clean the glass basically every day now again for the past few days... It's lightly stocked as I'm in the process of adding the fish (2 small clowns, firefish, flame hawk). It was the standard brs gfo, not the high capacity. I'm wondering if this initial round of gfo got spent quickly as there was probably a bunch in the tank when I added it? I also added the full recommended amount for a 75g. Does anyone think it's likely the gfo or should I look at something else? Nitrates are about 25.

 

[Sk8r]

It's possible, if it's getting bad again.

Your resupply of phosphate is either coming from the water source (using ro/di?) or is leaching out of the rock and sand, which can go on for a while. Once your medium depletes and the slow dissolving of phosphate out of the rock continues, you can be seeing the level rise again.

 

[DrBoxedWine]

Ahhh ok. I'm using Rodi. My rocks are BRS reef saver, and my sand is Tropic Eden reef flakes. How long does phosphate typically leach out of these sorts of things?

 

[Sk8r]

I had some laden holey limestone that leached for about 6 months. When I got to thinking on the why-it's-not-worrking and started changing the media every month, it took 3 months to fix it. I'm no chemist, but I suspect the water can only 'carry' so much phosphate, and when it can take more, more soaks out. So the more you pull from the water, the more you pull from the rock that's hosting the algae. When the rock runs out, the algae starts dying. My recommendation is one load of medium per 50 gallons. Phosban sells a larger reactor that holds 2 loads at once.

 

[Vinny Kreyling]

"The Shadow Knows'
Seriously, no one knows, you would have to put a rock in some fresh salt water & let it sit overnight & check the PO4 level to see if it is the rock.
Every time you add food you add PO4, it's a building block in nature.
The best way to tell when it is time to change it is to measure the water coming out of the reactor compared to the tank water. If it's close or the same it's time to change it.

 

[Sk8r]

Testing the reactor effluent is a really excellent recommendation, Vinny. Good one!

 

[Vinny Kreyling]

They show up once in a while!

 

[dkeller_nc]

I'm no chemist, but I suspect the water can only 'carry' so much phosphate, and when it can take more, more soaks out. So the more you pull from the water, the more you pull from the rock that's hosting the algae. When the rock runs out, the algae starts dying.

The physical mechanism you noted isn't quite right from the physical chemistry aspect, as seawater will hold a really large amount of dissolved phosphate compared to what would typically found in an aquarium, but the practical aspects are the same. Calcium phosphate dissolves quite slowly in seawater above pH 8.0, so it takes a while for it to get completely leached from the rock/sand surface, and if the tank water concentration is allowed to rise, that dissolution is even slower. So continually removing it from the water via chemical adsorption on GFO is the way to go.

 

[Sk8r]

Thank you, dkeller! Appreciate the backup!

 

[DrBoxedWine]

Thanks everyone. So I just took a measurement of my phosphates out of the sump before it even gets to the reactor and they tested at 0 via my salifert test kit. I tested some water I soaked their dinner in and it registered at 1, so I don't think the kit is bad.

Any suggestions on what to do? They tested at 0 before this as well, but I was getting a lot of hair algae so I just assumed it was being bound up in that.

So i'm not sure what my next move is. Anyone have any suggestions?

 

[shesacharmer]

Is your GFO moving freely in your reactor? Packing too tight reduces it's efficiency. Did you mix it with carbon? I'd go ahead and change out the GFO early and see if that helps.

 

[dkeller_nc]

Well, one issue that you have is that your test kit really won't measure phosphate concentrations at a low enough level. Most folks would like their reef tanks to have no more than 0.1ppm free phosphate, so we tend to use the Hanna Checker 713 meter and reagents. The photometer in the Hanna Checker will allow quantitation of phosphate at levels that are well below what our eyes can discern by comparing the test vial to a color chart.

 

[DrBoxedWine]

Yeah that's on my to-buy list, just have been putting off spending the cash. The salifert goes down to 0.03, however. There is even enough of a difference between 0.00 and 0.03 on the color chart that you could probably get an intermediate reading there too.

 

[DrBoxedWine]

Is your GFO moving freely in your reactor? Packing too tight reduces it's efficiency. Did you mix it with carbon? I'd go ahead and change out the GFO early and see if that helps.

And yeah I've got it barely moving like the brs website says to... Maybe I'll turn it up a bit this evening