0 PO4

[stevenVDB]

no matter how much po4 + I doses the tanks still reads 0

I dose 0.04 po4 daily on the doser. Outcome stays 0.
I’m testing with Hanna, tried different lot nrs
It’s been ongoing since a month now. Tester is still accurate, I’ve tested it with a buddy’s tank.

My tank is 6 months old.

 

[allof fish]

Did you start with dry rock? Do you have any algae issues? Dry rock tends to absorb phosphate for awhile in a new tank. How many corals to do you have

 

[stevenVDB]

Some new cycles (7weeks) dry rock was added 2 months ago.
I have about 20 corals. Some SPS’s are showing STN

 

[allof fish]

Some new cycles (7weeks) dry rock was added 2 months ago.
I have about 20 corals. Some SPS’s are showing STN

What are your other parameters. What lights do you run and how big is tank. What does your bio load look like. 0 phosphate won’t necessarily cause stn in acros sometimes just dulls them out. Too much phosphate can inhibit growth

 

[Gumbies R Us]

I'm also curious to know more information about your tank

Photo of your tank?

What are you using to test?

 

[stevenVDB]

What are your other parameters. What lights do you run and how big is tank. What does your bio load look like. 0 phosphate won’t necessarily cause stn in acros sometimes just dulls them out. Too much phosphate can inhibit growth

Nitrate is at 18
These are the other
Tank is a Red Sea 425 g3 with 115 G2 LEDs

About 10 small fish. 4 doctors and a cleanup crew

 

[BryanM]

This thread talks about DIY phos dosing.

Thread 'DIY Phosphate Dosing Recipe'

May 3, 2025

Sometimes phosphate can be so stubbornly low that the only way to meaningfully raise it is by directly dosing phosphate.

When you feed foods, you’re adding nitrogen, carbon, and loads of organics. This effect is compounded if you’re trying to offset rocks that initially work against you by binding up most of the PO₄ until a higher equilibrium is met. It’s much cleaner and more cost-effective to purchase pure sodium phosphate online than to use hobby-grade products with unknown purities and byproducts.


You can mix sodium phosphate with nitrate, ammonium, or even add it to an ATO...

• Miami Reef
• Replies: 78
• Forum: Reef Chemistry by Randy Holmes-Farley

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[allof fish]

Nitrate is at 18
These are the other
Tank is a Red Sea 425 g3 with 115 G2 LEDs

About 10 small fish. 4 doctors and a cleanup crew

Nothing wrong with those numbers. It’s hard to believe that your phos just disappears especially after dosing. I would take a sample to lfs just to check as maybe your tester is bad. (Ik you check with your Friends tank) or just rock is just not 100% stable and sucking up and realizing phos every so often. If your nitrates were very low I would be more convinced but since there at 18 it’s kinda odd

 

[Randy Holmes-Farley Verified Community Expert]

no matter how much po4 + I doses the tanks still reads 0

I dose 0.04 po4 daily on the doser. Outcome stays 0.
I’m testing with Hanna, tried different lot nrs
It’s been ongoing since a month now. Tester is still accurate, I’ve tested it with a buddy’s tank.

My tank is 6 months old.

It can be very hard to bring phosphate on scale as a lot binds to rock and sand.