I have a new 75 gallon setup. 3 months old. CaribSea Live Sand and LifeRock. Everything seemed to cycle well. Had an ammonia spike followed by nitrite and nitrate. Everything dropped down to nil after a few weeks of water changes. Let everything sit for almost a month then added cleanup snails and hermies. Had fish for a little over a month. 8 Blue Green Chromies, 2 Clownfish, Coral Beauty and 2 Mollies (saltwater acclimated). Everything was going well. Had a dirty phase which lasted about a week. I added some cheto to sump and everything cleared up. Sunday Ammonia, Nitrite at 0, Nitrate about 3.5. Then on Wend one of the mollies and a chromie died the same day. Did a water test and my Ammonia was at 1ppm, Nitrite 1ppm Nitrate 5ppm. Wend and Fri did a 25 gallon water change and my numbers were at Ammonia 0.25ppm Nitrite 0.5ppm Nitrate 5ppm the next day. On Monday did 30 gallon water change and I'm still at Ammonia 0.25ppm, Nitrite 0.25ppm Nitrate 10ppm. Testing today the numbers are still the same. No change since before the last 30 gallon water change. Would have expected some change. The rest of the fish and cleanup crew seems to be thriving. They are eating well. I am feeding frozen brine shrimp 6-8 times a day but small amounts. Enough for them all to eat in 30 seconds. So they are not leaving much waste behind, and the clean up crew does a great job. But the numbers are not changing. Any advice?