Habitat - Indoor :: nitrate level spike after water change?

[scripta_elegans]

I did a 80% water change today, and suddenly the tank became cloudy. I tested the levels, and the nitrate levels came back higher than I have ever seen them. I cleaned the filters about 3 weeks ago, and I have 2 XP3 filters for a 125 gallon tank. One turtle, no other animals. What happened? I will do water changes for the next week to try to get the levels down, but any guesses on why this occured? It did occcur to me that the levels might have been high before the water change, but why would the water not be cloudy until afterward? I tested the tap water as well, and it tested as zero. The Ammonia and Nitrite levels are non existant, and the PH is 7.4. What is going on? Pics below.

[steve]

An 80% change would have removed a lot of what would be in there, so could something have happened to the bio media? What was the nitrate level?

[scripta_elegans]

It was the test kit. I realized that I hadn't let the tap water sit long enough. After I did, it turned bright red too. I got new test chemicals, and it was at about 5 ppm. I really was going nuts though. The level measured the same beofre and after the water and filter change, so my hypothesis is that as the test kit ages, it might react to the full extent if there is any Nitrate in the water at all. Here are some pics of Spike from a few days ago though! (Her water is crystal clear again.)

[VeipaCray]

It's always the test kit

I switched over to one of these years ago... never looked back.
http://www.aquacave.com/pinpoint-nitrate-monitorbr-by-american-marine-1567.html