weird nitrate drop?

[salajander]

Hi all,

After being ~6-8 ppm for the last 9 months or so (last test before this was jan 22, 6ppm), my nitrates are suddenly showing essentially 0 after testing last night. I normally use Red Sea, and did it twice because I didn't quite believe it, and then I double-checked with a Salifert kit I had around. Both showed essentially 0.

I have a 55g display, 10g sump (with around 5g in it) and a 5g refugium. Probably around 60g total volume.

I've been battling cyano, so I've been doing a bit more water changes than normal (10g on jan 25, 5g on jan 31, then 10g two days ago), but the volume alone would only have dropped it from 6 to just under 4.

I also just started a lights-out for the cyano, and the 0 ppm test was after 1 day in the dark...

And that's not considering normal build up over time or how much detritus I've stirred up by blowing off rocks and scraping the walls.

I know low NO3 is a good thing generally, but I also know that nothing good happens quickly in a tank, so I'm sort of surprised to see my NO3 drop so quickly.

Any ideas?

[Timfish]

Something ate it. I would want to confirm the test kit is good but I have seen surprising drops over the years and still don't really have a good explanation (once was a drop from 160 to roughly 0 in 12 days after a 10% water change and confirmed it with two different test kits). I have found the nitrogen cycle is very, very complex with the coral holobiont fixing and conserving nitrogen for the coral. Phosphate is also needed for coral to make use of nitrates for their symbiotic diniflagellates so I wonder if you added some phosphate with the water changes, have you tested your tank, makeup and source water for phosphates?

[salajander]

Phosphates have been pretty steady at the low end of the Red sea tests (0.02 PO4/0.007 P-PO4). That's where they tested yesterday, too.

[salajander]

And as far as the test kit goes, as I mentioned I tested with two kits from different manufacturers, both reported near-0.

Like I said, I'm not really complaining about it, it's just surprising and I don't understand what would have caused it.