Cycling question - unexpectedly quick nitrite/nitrate readings

[Agent Kooper]

I've set up a 12-gallon nano tank. I put in about 15 pounds of live sand (purchased in a bag from Petsmart), 15 pounds of base rock (CaribSea fossilized/petrified reef rock) and the water two weeks ago.

About a week in, I poured in a bottle of Bio Spira, just for the hell of it, and because I didn't really know what I was doing. I've been measuring the water, also just for the hell of it, getting 0 ammonia/nitrite/nitrate -- exactly what I expected because I don't have an ammonia source yet.

I decided to put in one raw shrimp to start the cycle. I did this 24 hours ago. I just measured the water and got a reading that surprised me: no ammonia (that's not the surprise, because I know I was impatient on the test), but 3 ppm nitrite and 40 ppm nitrate.

I don't know how I'm possibly getting nitrite and nitrate readings at this point -- I was just looking for the first signs of ammonia. Is it possible my live sand and the Bio Spira already started cycling my tank before I added the shrimp?

This is my first marine tank, but I've been educating myself and these results surprise me given what I've read.

 

[SushiGirl]

Yes, it's possible there was die off in the sand and it provided an ammonia source.

 

[acrab78]

Yes, it's possible there was die off in the sand and it provided an ammonia source.

+1
I would go ahead and do a good waterchange the nitrates are getting up there.

 

[SushiGirl]

I wouldn't do a waterchange yet, the presence of nitrite shows you're still cycling.

 

[disc1]

Also keep in mind that you can't trust a nitrate reading if you are also reading nitrite. A little nitrite will show up on most nitrate tests as a large amount of nitrate.