First, stop adding the Nitraban. You've got plenty of bacteria in there if you have a bloom going. Also stop adding the PH adjuster. That stuff is worthless. If you REALLY need a buffer, I agree with the crushed coral method.

Stresszyme is fine.

Definitely pick up an API Master Freshwater Test kit ASAP. It's expensive, but it's well worth the money for it's accuracy and thoroughness. Right now I think you definitely need to test your ammonia levels (which the kit has), because if there is a little nitrite and no nitrate, I'm suspecting you have a very high amount of Ammonia right now, which would account for the bacteria bloom.

I second getting Anacharis (Elodea) and/or Hornwort to help level out and soak up some of the ammonia. Keep doing water changes every couple of days or so like Nurse Platy said, and checking the water before you do one and write down your numbers.