So I have had a 20 gallon tank set up for close to 6 weeks now. Went through the cycle, ammonia spike then drop to 0 while Nitrites spike. Nitrites gradually dropped off to 0 and have remained there for the last 3 days or so. Did a water change tonight and God down with the siphon and tried to really clean out the gravel good. Only did a 5 gallon change. Let it sit for a couple hours after the change and go back to check on it and notice that the water is a bit cloudy. Did a water test. Nitrites are still 0 but there is a trace of ammonia...about 0.25. Is this something I should be concerned about or is it common for a tank that has cycled??