I set up my 33 gallon/ 128 liter tank 5 weeks ago. For the first 4 weeks I only had 2 Zebra Danios and several live plants in there. A week ago I added 3 young Platies after I finally QT'd them. The Platies especially are avid poopers, and when I vacuumed the gravel yesterday, I found tons of waste. I've been doing 30% water changes weekly (first to dilute the salt I added when I thought the fish were sick, then to remove some of the waste that was building up, and to dilute the brown water that adding a Mangrove root caused.) But at no point have I registered any ammonia, nitrites or nitrates in the water. With only the Danios, I thought they weren't producing enough ammonia. Now with the Platies added, it seems like there should be enough waste produced for that. I've started suspecting if I can trust my tests, but then again, the fish seem happy, so there couldn't be much ammonia or nitrites around (I bought the Freshwater Master Test Kit, and a separate Nitrate test from the same maker on my trip to the U.S. 2 months ago.) The water, including the pH, has been stable all along. Do I really need some nitrates to prove my tank has cycled?