The Nitrate was what I felt is probably too high. If your nitrate is 80 you will have water quality problems. Are you doing water changes? How much and how often? You said your tank looked better after your big
water change when moving, for a few days...this tells me that if you upped your waterchanges it should help.
Your tank is only about 35 gallons, and you haven't' said how many of each fish you have, or what kind.
With the rule of thumb for stocking being 1" of adult fish per gallon, you have to figure what your fishes expected max is suppose to be. It makes a huge difference if you have bala sharks, iridescent sharks or redtail sharks. It also makes a HUGE difference if you have a common pleco or a bristlenose pleco. To sort this out, you really have to address these issues.
An overcrowded tank will have high nitrates, and be hard to keep clear.