Question about refugium uptake ratios of nitrate and phosphate

[Beats001]

Hi,
My refugium is doing wanders for nitrate levels, but not much for my phosophates, I'm interested in other peoples experience in this regard.

My nitrates started to bottom out, so I dosed potassium nitrate to bring my levels up to 3ppm.
My phosophate, sits at 0.15 - 0.2.

My nitrate went down from 3 to 1 in about 4 days and phosophate didn't seem to move.

Kits I am using are red sea for both nitrate and phosophate.

What should I do?

 

[andrewey]

Randy has a great question about the weight ratio (and not the ratio of atoms) on this exact topic a few years ago. The average ratio is around 20:1, although this differs between species and can change depending on whether the tank is nitrate limited or phosphate limited. It's a bit different then the redfield ratio.

 

[Beats001]

The average ratio is around 20:1

I have read 50:1, so by that logic if my nitrate is reduced by 2 ppm in 4 days, my phosphate should be down .06 if my maths is correct.
Thats not happening if my test kit can be trusted.
Or I am adding too much phosphate some how.

Meh

 

[andrewey]

As I said, it depends on the species- the average is closer to 20:1 than 50:1, but that depends on which macro's you are averaging and the levels within your tank. For example, from the post described above, you can see how they differ:

 

[andrewey]

That image comes from this paper- you might consider reading the discussion which is pretty good:

https://web.archive.org/web/20040720161739/http:/www.botany.hawaii.edu/Bot482/Kaneohe Bay algae N-P Larned Mar Biol.pdf

 

[Beats001]

Interesting. No Chaeto in that list.

 

[Beats001]

That image comes from this paper- you might consider reading the discussion which is pretty good:

https://web.archive.org/web/20040720161739/http:/www.botany.hawaii.edu/Bot482/Kaneohe Bay algae N-P Larned Mar Biol.pdf

Good stuff, some toilet reading

 

[andrewey]

Interesting. No Chaeto in that list.

Unfortunately, I can't send you the pdfs directly, but you should be able to download the first pdf if you google "chaeto linum effect of nitrogen and phosphorus supply on growth" and select one of the first few sources that is a pdf. I'd be more than happy to figure out how to find the pdfs of papers if you're interested.

 

[ReefGeezer]

You also have to consider the phosphate bound in the substrate. It will return to the water column as the Cheato uses phosphate. This may make it look like the phosphate is not being used in a reasonable ratio. Biology says it is, but we don't see it because it is immediately replaced. This could continue until the level bound to the substrate falls.

 

[Gablami]

It’s also possible that whatever you’re adding to the tank (fish or coral food) may be higher in phosphate relative to nitrate...

I’ve also had this problem in the past. Chaeto seems to bring down nitrates more easily than phosphate. Not sure why. I wish I didn’t need to use GFO, but I do.