How do you keep nitrites and nitrates down in a hospital tank?

[slider162]

My nitrites are at 2 and my nitrates are at 50 tonight. It has been 2 days since my last water change. I do a 15-20 gallon water change every 2-3 days in a 50 gallon tank (bare bottom with pvc). I dose Amquel+ and have two power filters filled with de-nitrate by seachem and a bag of Bio Chem Zorb.
Stock:

Majestic Angel
2 True Percs
Flame Hawk
Skipper Blenny

The only thing I can think of is to feed every other day. How does everyone with a bare bottom keep these parameters under control? Can I overdose with Amquel+? I only have 3 more weeks of this, but I am going through a heck of a lot of water and salt. Thx

[NeveSSL]

It would probably take a few days to take effect, but what about a remote deep sand bed?

Brandon

[Amphiprion]

Do you vacuum the bottom regularly? It is a must with quarantine/hospital tanks. Also, don't worry about nitrite or nitrate--they both are of little concern. You should worry about salinity, pH, and ammonia (especially the latter).