A little over a week ago we found Ammonia in our 75g cycled tank. The only new additions in the last month were 1 Bristlenose and 2 Mystery Snails (both of which have died). The tank was started in February and we slowly added fish and began to see 0 ammonia/nitrites and a health amount of nitrates! We've vacuumed, moved everything, did tons of water changes, ADDED a Fluval 406 for additional filtration and we still have Ammonia! GRRR! I am completely at a loss of what is causing this problem. How do we get rid of this ammonia? BTW, our nitrates are currently fairly low, most likely due to all the water changes.