Nitrites of .25 may be of some concern but not time to panic. Keep checking. You can add some salt if they go higher but if .25 is the max I wouldn't worry. I forgot what the salt dosage is.
I have a book on Fish Disease. It say's that nitrites of 10 is where toxicity starts.
There are resins that take amonia,nitrites and nitrates out of your water. You put them in your filter. Fluval makes one, Nitrasorb is another. They do work but not in hours but days. Don T.
I had a similar problem. I thought the tank had cycled but I added fish and the bacteria couldn't handle the load. My nitrites went up to 5 and it took abought two weeks to get it back to normal Don T.