Sudden drop in Nitrates - why?

[WallysWorld]

For the last several months my Nitrates have been very stable around 2ppm. Got refill reagents for my Red Sea Nitrate Pro Test Kit. First test and and nitrates are undetectable. Double check with last of old reagents and they also tested zero.
Haven’t done anything different to tank. Standard weekly water change is all. Same feeding regime.

Why the sudden drop in a week since last test?

 

[Reefing Madness]

 

[Dan_P]

For the last several months my Nitrates have been very stable around 2ppm. Got refill reagents for my Red Sea Nitrate Pro Test Kit. First test and and nitrates are undetectable. Double check with last of old reagents and they also tested zero.
Haven’t done anything different to tank. Standard weekly water change is all. Same feeding regime.

Why the sudden drop in a week since last test?

I don’t find that unusual but that does not answer your question.

Finding the cause is unlikely. Think of the hundreds of microorganisms vying for nitrogen. A “little” thing like a change in another nutrient, such as a phosphate increase, could suddenly enable those hundreds of microorganism species to need more nitrogen. A burst of of micro alga growth might wipe out 2 ppm of nitrate and you might not even notice the increased in green anywhere. Maybe your coral started growing more rapidly.

If you find the 2 ppm level important, dose sodium nitrate. @taricha manages his nitrate levels and will share his nitrate level plots showing the swings that nitrate concentration can take.

 

[taricha]

For context, I find that after tracking for months, most of the time my tank eats 2ppm NO3 per day! So to me that's not a significant amount. Not even enough to know for certain that it's a real effect.
My line of thinking is like Dan's. a mini surge of some organism that consumed more NO3. But I'll add that you did a water change and possibly added some limiting element, allowing a previously limited organism to grow faster.

 

[WallysWorld]

I'm guessing that my point of reference is off....when you only measure 2 ppm of nitrate for months, a drop to zero seems like a lot! Need to reset my expectations.

Thanks for the help!