Nitrite mini-spike is over but low level ammonia persists -- why?

I recently moved 18 African Cichlids and two small pleco's from an
established 20 gallon to a used 35 gallon tank I bought. The tank is
nowhere near as over-populated as it might seem as the African's range
from 3/4" to 11/2" long. Now I screwed up my bio-filter by not
realizing the danger of rinsing everything in (chlorinated) tap water
-- including the bio-wheels on the Emperor 400 that came with the used
35 gallon setup! The gravel from both tanks was pretty nasty as was
the Emperor 400 -- that's my only excuse for the over-zealous washing.
Once I realized what I had done I added some gravel from the used
setup I had acquired -- still in a pail with the tank water from the
(very highly) used setup. So I had at least some undisturbed seeding.
I bought to pouches of Bio-Spira from two different LFS's -- trusting
that at least one would have escaped poor shipping/handling practice
-- and slowly poured the contents over the bio-wheels. My fish are
showing NO signs of stress and have voracious appetite. The nitrites
promply went down from .25-.5 to 0 but the ammonia persists at about
..25. Ph is about 8.4, hardness about 10. I am using two different
test kits with identical results. Both are the type where yellow=0,
dark green=death. One has two test chemicals and the other uses
three.
I am puzzled why the ammonia remains after the nitrites are gone.
Isn't this backwards?
I have not used "ammo-lock" but the new water conditioner has
something similar in it.

Don in Austin