hmm, i feel like you messed up your biofilter somewhere along the way? has there been any low PH reading? over clean filter media? anti-bacterial medication?
i'm not sure if metro affect nitrate but metro is sugar base, will spoil the water quickly.
Stability won't hurt but work or not, we never know :|,
SAFE and PRIME are your best friend during mini cycle imo, more wc ... good luck.