ok i have a question about my water conditions. every week i do a 50% water change,i usually check my parameters once a month but 2 weeks ago i added some new stock and thought i should check , so my parameters are as follows, ammonia 0,ph 76,nitrites 0, nitrates 0-maybe 2?, my tank houses 4 juvenile flowerhorns, a raphael cat, a blood parrot and 2 adult(very large) Oscars. why do you suppose my nitrates are 0? and i am running a Fluval FX5, was thinking maybe i should just do a vacuum only today and check again in a couple days? fish seem fine, very active and appetites are voracious!