My 55gal tank has been set up for 5 weeks now and my ammonia spiked, followed by the nitrites and nitrates and my ammonia went back down to 0 and all other levels 0. Now, my ammonia is creeping up to .25 again. Is this something I should worry about or what do you think is happening? I have 4 adult guppies in there right now but I was hoping this week to put in 4 1.5 inch piranha's. Is the tank ready for this change over?