checking phosphates soon after feeding.

[Jej34]

Ok so I check my phosphates before feeding this morning and come up with 0, using a Hanna phosphorus ulr. I just fed some mysis (1/2 cube in a 72 bow) and just got a reading of .40 a half hour after feeding

Normal?
Is there a rule of thumb to check after so many hours after feeding?

 

[Randy Holmes-Farley Verified Community Expert]

I've not seen this sort of variation, and am a little skeptical it is real. It may be testing error.

Half a cube of what?

A half cube of prime reef would only boost phosphate to 0.02 ppm even if every bit of phosphorus ended up detectable in the water after 1 h, which seems unlikely.

I show that here:

http://www.advancedaquarist.com/2012/3/chemistry

 

[Jej34]

I'm looking at the surface of my water and there's a lot of dust particles I think due to a water change yesterday. Sand possibly. I'm wondering if that debris got in the tube and skewed the numbers.

I'm going to check the link that you sent me.

Thanks

 

[Randy Holmes-Farley Verified Community Expert]

Yes, light scattering in the test will look like more absorption due to phosphate.