Erratic Phosphate Levels

[Jrapa86]

Hey everyone, I'm experiencing some difficulty I was hoping you could shed some light on. I'm trying very hard, and open and flexible to any suggestions.

I'm experiencing erratic and varying phosphate levels. I cannot seem to maintain consistent levels ~ 0.01-0.05. Instead, I either bottom out at 0 or go as high as 2. Three days ago, I was at an all-time high of 4.0. Yesterday, with these settings below, I was at 0.05. The day before, I was at 0. Today I'm at 1.26. If I change (increase) my GFO / Skimmer timing, I bottom out to 0. If I go in the other direction, I end up too high.

I don't think it is my Hanna phosphate checker because I'm constantly battling a stubborn dino / brown hair algae problem, delayed coralline growth (still minimal growth), and unimpressive coral growth.

Setup:

Age: 1.25 years mature
65-gallon DT / Total (w/ sump): 84 gal
Automatic Doser: Red Sea No3-Po4X : 6.7mL / 24 hours
Carbon/GFO Reactor: Timed on/off with Apex: 19:00 to 23:00 ON (4 hours), and 07:00 -12:00 ON (7 hours)
Skimmer: 19:00-12:00 ON (17 hours)
Auto-Feeder (Apex): 1 Feeding (Flakes) per day, 3 drum rotations.
Manual Feeding: 1x Daily (evenings): LRS Reef Frenzy frozen food: 1in x 0.7in x 0.2in piece.
Macroalgae: 10gal section of sump right after the filter sock and before the skimmer, separated by a baffle, is the majority chaeto filling that section, with biobricks for pods at the bottom.
Water Changes: 3.0 gallons / 24 hours with Apex DOS AWC. Last manual water change of 20% 2 weeks ago.
Additional: 2 bags of carbon under the baffle going into my return chamber of the sump

I am stumped on maintaining acceptable phosphate levels consistently NEAR but not AT 0.
Things I'm wondering on the side: how much of an impact does the skimmer make on Phosphate levels, by the way?

 

[taricha]

What does the hanna cuvette look like when it reads high PO4? visibly blue? cloudy?

Do you have a sandbed?

If I change (increase) my GFO / Skimmer timing, I bottom out to 0. If I go in the other direction, I end up too high.

If you had GFO in a reactor and left it off for hours or a day, it might do something unexpected when you turn it back on.

 

[Jrapa86]

What does the hanna cuvette look like when it reads high PO4? visibly blue? cloudy?

Do you have a sandbed?



If you had GFO in a reactor and left it off for hours or a day, it might do something unexpected when you turn it back on.

The cuvette today had a hue of blue to it after I added the reagent. Usually, it appears clear. Not cloudy.
I have a sandbed in the DT.
That is a great point on the GFO. The problem is I believe if I run the GFO constantly, it will bottom out my PO4 to 0.

 

[chipmunkofdoom2]

First, I would rule out testing error. I would order a calibration kit. Hanna sells two-vial kits that come with pre-mixed solutions that allow you to confirm the accuracy of your Checker.

If the readings are accurate, I think part of the problem is the chaeto and organic carbon dosing (though organic carbon doesn't need very much PO4, the bacteria can't reproduce without it). You can't turn these methods on and off like a switch, like the GFO. They're organic, biological processes.

When your PO4 bottoms out, likely after you run your GFO, your chaeto and bacteria can't grow anymore. Since they stopped growing and your GFO is off, PO4 starts rising. As PO4 rises over time, the chaeto and bacteria will begin to grow, but it's not immediate. It's a slow ramp up. So for a while after you shut off your GFO, nothing is using the PO4. Which could allow it to climb

I would gradually cut back to one PO4 reduction method. I would probably choose the chaeto as it's the simplest and self-regulating. Hopefully that will make things easier to troubleshoot.

 

[taricha]

The cuvette today had a hue of blue to it after I added the reagent. Usually, it appears clear. Not cloudy.

Sounds like the kit is working correctly.

That is a great point on the GFO. The problem is I believe if I run the GFO constantly, it will bottom out my PO4 to 0.

I would adjust by restricting the flow down further and further (or lowering the amount of GFO way down). On-Off seems to be giving weird and undesirable results.