I also set up 3 smaller tanks with new Amazonia mid December. Two 10G and one Fluval Flora (7.9G). One 10G with about 3" of substrate covering the entire bottom, it's still leaching, I didn't use any old filter media in that tank. The Flora is the same, with less substrate about 2". Both tanks are still high in ammonia about 4 ppm. The other 10G I have a small divider about 3", I only fill the smaller side about 1/3 of the tank length. For this one I added matured filter media, and it had very close to 0 ammonia in about 2 weeks.
I'll still be patient though, not planning to add shrimps for another 3 weeks at least.