I did it! Goodbye blue, hello natural honey color!
It was a lot more disgusting than I thought to remove the gravel by hand, and I am having trouble replanting one of the plants, but I think it's going to turn out to be worth it once I add some new plants. (It looks very bare and bland now compared to the blue gravel. I am in desperate need of some more greenery!)
I left the old filter cartridge in the tank, along with about a pound and a half of old gravel in media bags. This morning I did water tests, and here's what I got:
Ammonia - I couldn't tell if it was 0 ppm or a little more. I am guessing it was around .05 ppm. The lowest reading on the key, other than 0, is .25, and it wasn't even very close to that.
NitrAtes- 10 ppm
I don't know if the tank if going to go through a cycle all over again or if the presence of nitrates means it isn't going to. What do you guys think?