Increased nitrite in QT

[cbrine]

So I have a 10gal QT with a sponge and ceramic bio cylinder type material in the filter (was running a week or so in my DT so help jump start the bacteria prior to putting it on my QT). I test my water daily and cycled tank with water from my DT. Water changes done weekly with freshly mixed water. About a week or so after setting up purchased chromis, a firefish and a diamond goby. Only lost one chromis to abuse? Otherwise the rest look well. I noticed end of last week my nitrite levels have been increasing but everything else remains good.
Temp:74, sal:1.025, kh: 8, ca:360, no3:0, ph:8.4, PO:0, nh:0
I was doing 10% changes daily which did nothing and then started doing 50% daily still with no major drop. I feed once a day of flake food. Tank is all glass with a few plastic pipe pieces that was boiled to sterilize. Anyone have any tips to help reduce my nitrite? After my water change (50%) I got 0.25. Help?