GFO Phosphate issue

[Tokyoyankee]

hi all

I'm running a 90g SPS tank. I've been testing my phosphate levels which are running at 35ppb and no matter how much GFO I add, it never drops. I'm assuming that the rocks are leach phosphates. I've even added 30 drops of lanthanum chloride for the past week and still my phosphates are consistently running at 35ppb. I feed two frozen mysis cubes and dose the full range of Aquaforest coral supplements daily.

I'm running roughly 1200 grams of GFO in two TLF 550. I'm dosing 10ml of a mix of vinegar and vodka 70/30 ratio.

I have two questions

1. My PO4 test reads 35ppb for the tank but 39ppb for the output of the GFO reactor. Why? I'm assuming the GFO is exhausted but why would it give a higher reading?

2. What is the best course of action? Large WC to drop the levels?

Thank you in advance for any input

 

[Giovanni]

What test kit maker?
Could be a faulty test kit?

 

[drawman]

+1 may try to crosstest with another sample and/or test kit.

 

[Tokyoyankee]

Hanna Checker 736

 

[jda]

Yes, it could be the rocks. They are not leaching it, but rather unbinding it as they get into equilibrium with the water - they are doing their job and one thing that calcium carbonate does very well. It can take a while, but it will come down. If you used dry rock, it can take 8 months to a year for some. If you have an older tank, then that depends on the bioload that you have had in the tank over the years. Rock from the ocean is typically free of phosphate since there is next to none in the water for it to bind with.

Basically, the calcium carbonate will bind with PO4 until it is saturated. Then, the levels just rise in the water column. You can get the water column numbers down quickly with the GFO until you reach the saturation level of the rocks, and then it is slower. In your case, this could be 35 ppb.

Don't forget about the sand Sand is easy to remove and replace that will really help. I start to replace my sand in year 3 or 4 of a tank and change about 25% every 3 months... then repeat in 3 or 4 more years.

If you do change the water, time it with a GFO change. The GFO will release PO4 back into the water to achieve equilibrium too, so you want fresh GFO after a water change.

With the hannah checker, they are pretty accurate as long as you are cleaning the vials VERY well, including the bottoms, when you are testing. You can check your tester by using 2 vials of tankwater - should read zero, or very close to it.

Carbon dosing has never helped me with PO4, but it does really well for NO3. You should not have a NO3 problem in a reef tank or you have much larger issues.

 

[Tokyoyankee]

Yes, it could be the rocks. They are not leaching it, but rather unbinding it as they get into equilibrium with the water - they are doing their job and one thing that calcium carbonate does very well. It can take a while, but it will come down. If you used dry rock, it can take 8 months to a year for some. If you have an older tank, then that depends on the bioload that you have had in the tank over the years. Rock from the ocean is typically free of phosphate since there is next to none in the water for it to bind with.

Basically, the calcium carbonate will bind with PO4 until it is saturated. Then, the levels just rise in the water column. You can get the water column numbers down quickly with the GFO until you reach the saturation level of the rocks, and then it is slower. In your case, this could be 35 ppb.

Don't forget about the sand Sand is easy to remove and replace that will really help. I start to replace my sand in year 3 or 4 of a tank and change about 25% every 3 months... then repeat in 3 or 4 more years.

If you do change the water, time it with a GFO change. The GFO will release PO4 back into the water to achieve equilibrium too, so you want fresh GFO after a water change.

With the hannah checker, they are pretty accurate as long as you are cleaning the vials VERY well, including the bottoms, when you are testing. You can check your tester by using 2 vials of tankwater - should read zero, or very close to it.

Carbon dosing has never helped me with PO4, but it does really well for NO3. You should not have a NO3 problem in a reef tank or you have much larger issues.

Thank JDA

Can GFO leach PO4 back into the water once it's fully saturated with PO4?

 

[jda]

GFO will absorb to equilibrium. If you don't change any water, then it will stay where it is. Lower the PO4 in the tank water and the GFO will unbind some until they are at equilibrium again.

 

[Tokyoyankee]

I did a 30 percent WC and changed the GFO. I tested the water column and got 24ppb. 6 hours later, I tested again and its back up to 34ppb. I haven't fed since the WC.

Should I continue to do large WC to continuously drop the PO4 levels?

Thanks in advance

 

[jda]

How old is your tank? How old is the rock? Where did it source from? How old is the sand?

Is

 

[Giovanni]

Make up some new salt water in a container large enough to hold a large piece of your display rock. Test test the new water for Phosphate. Rinse the test rock in separate freshly made Salt water before putting it in the test container. Place your rock in the container with a pump for circulation. Retest Phosphate every 12 hours and see what you get. If no phosphate shows up, try your sand the same way.

You could have phosphates coming in through your RODI unit as well. I would test it.