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neiltus
11/07/2016, 01:41 PM
Been running GFO to get PO4 down, not wanting to over do it, I have been testing sometimes 2x a day.

I have noticed that when lights are on, my PO4 can test much lower, and in the mornings after my lights have been off for 10 hours, my PO4 sometimes tests higher.

Curious if there is a known relationship between lighting and algae uptake of nutrients? I know ph can raise due to photosynthesis but would this effect PO4 that is testable in the water column?

Today my PO4 tested via Hanna at .23 at 6am, at 2:30, it tested .09

bertoni
11/07/2016, 02:52 PM
The plants likely are growing a lot more strongly during the day when the energy is going into the system. I'm not all that surprised about a nutrient increase over night, although I have no idea how many tanks will show a change that we can measure with our kits.

Dan_P
11/08/2016, 01:42 PM
A good start to answering the question is to separately average the test results for the two photoperiods. Then calculate the standard deviation. If the average values are close, e.g., fall within two standard deviations there might not be an effect. There is a rigorous way to compare two averages which I don't remember.

I have been wondering about this myself. You have encouraged me to give it a look.

Dan_P
11/10/2016, 04:15 AM
I am running PO4 tests today, but did a quick look into "diurnal absoption of phosphate by algae" with Google:

Night absorption of PO4 by freshwater algae articles:

https://www.jstage.jst.go.jp/article/jswe/20/5/20_5_338/_article

http://link.springer.com/article/10.1023/A:1008196308564

Coral Reef absorption roughly constant absorption, day or night article:

http://onlinelibrary.wiley.com/doi/10.2307/1935343/full

Dan_P
11/11/2016, 04:31 AM
Here is what my system's phosphorous level looks like over a 24 hour period. The x-axis is the time since the first measurement at 5 AM (t=0). Feeding might be the cause of the 12 ppb P maximum. Only way to tell for sure is to take more readings during the afternoon.

http://i1028.photobucket.com/albums/y349/Drfungus137/24%20Cycle%20P_zps39uqx6hx.png

Timfish
11/11/2016, 06:51 AM
Well, my two cents, the phosphorus cycle is pretty complex and we can only test for the inorganic form we colloquially call PO4 and corals will use either organic or inorganic. Some of the processes we need to take into account are: Phosphorus is needed for photosynthesis. Phosphorus is the limiting nutrient for corals to use inorganic nitrogen. Fish will be releasing phosphates throughout the day.

http://jeb.biologists.org/content/214/16/2749.full

Dan_P
11/11/2016, 01:40 PM
Well, my two cents, the phosphorus cycle is pretty complex...

Yes, a good cautionary note, but discovering trends is always a nice surprise and fun to speculate on and read about potential causes.

bertoni
11/11/2016, 04:07 PM
I'll have to check those links. That's interesting.

neiltus
11/11/2016, 06:27 PM
Well, my two cents, the phosphorus cycle is pretty complex and we can only test for the inorganic form we colloquially call PO4 and corals will use either organic or inorganic. Some of the processes we need to take into account are: Phosphorus is needed for photosynthesis. Phosphorus is the limiting nutrient for corals to use inorganic nitrogen. Fish will be releasing phosphates throughout the day.

http://jeb.biologists.org/content/214/16/2749.full

only read the summary (finish after kids asleep), but interesting....ty

SantaMonica
11/13/2016, 09:21 PM
You probably have a nice thick periphyton coating on the rocks, which is very photosynthetic and thus will pull in more phosphate when illuminated. Is very common and predictable on reefs.