Nitrates disappeared over night!

[Ringoffire]

I am at day 21 in fishless cycle in my 55g. Nitrites and nitrates showed up about 10 days ago. Dosing 1-2ppm ammonia daily. Nitrites and nitrates have been on a steady rise, and have performed 1 35%wc a week ago to bring nitrites down a bit. My problem now is that my nitrates have disappeared over night. Tested it 3 times to rule out test error with same results. Last 5 days of readings below can anyone give me an idea of how this could happen and what may be going on?

3/19. 3/20. 3/21. 3/22. 3/23.
Ph- 7.8. Ph-7.6. Ph- 7.6. Ph- 7.6. Ph- 7.6
Ammo- 1. Ammo- 0. Ammo- 1. Ammo- 0 Ammo- 0
Nitrite- <5. Nitrite- <5. Nitrite- <5. Nitrite- <5. Nitrite- <5
Nitrate- <20. Nitrate- 80. Nitrate- 160. Nitrate- <160. Nitrate- 5 ppm.
Performed 25% wc and dosed 2 ppm ammo

 

[Ringoffire]

Sorry really didn't mean to post twice.

 

[librarygirl]

Any live plants in the tank?
I've seen this before...have yet to find an explanation though. It's possible that nitrates are so off-chart that the color is matching back to a lower level, although I'm not sure. I wouldn't worry about it though; if everything else is still on-track, I would just continue the cycle.

 

[Ringoffire]

Yes there are 3 live small plants in the tank. Tested this morning and got the readings:
Ph 7.6
Ammo 1
Nitrite < 5
Nitrate 80
So apparently the water change brought the nitrate to a readable level but not the nitrites. I'm thinking it may be possible that they where so high the test couldn't even register. Who knows? I guess I'm still on the right track. Still wish I could get the nitrites down a bit to prevent the cycle from stalling. Guess I need to do a few more water changes huh?