I recently purchased a 45 gallon freshwater tank. It has been setup for about 2 weeks now with 6 guppies from an existing tank as well as various plants (Anubias Nana, Java Fern, Amazon Sword, to name a few). I have been testing the water using the API Freshwater Master kit, yet I am still not detecting any ammonia, nitrites or nitrates. Shouldn't the guppies have produced a detectable level of ammonia by now? Is it possible the plants are absorbing it?