Thanks for all the helpful responses!
My exact setup is a 24g JBJ Nano cube, it has an integrated filter on the back which functions essentially like a canister, with a strong powerhead pulling everything through. I have a couple sponges, some pillow filling in media bags, and two bags with ceramic biomedia in there. Lighting is 2x36w 6500k fluorescents. Substrate is Floramax, it's planted with some anubias, java fern, red foxtail, and rosafolia. I have a few pieces of small manzanita driftwood.
I had the tank running on a fishless cycle with the plants in starting at the beginning of April. I was doing the tank with Dr. Tims ammonia. I also added a bottle of Tetra safestart. I saw the nitrogen cycle play out to the point where ammonia was being completely eliminated, with some low level nitrItes and nitrAtes.
To help the plants I added the tabs about a day before I put the fish in. I followed this recipe: https://www.youtube.com/watch?v=CKXvejLWfF4
. It uses Miracle Gro instead of Osmocote, which is where I think I ran into my problem! I'm not sure, but I think there are about 10 in there.
I knew the tank was definitely not completely cycled when I decided to add fish last Saturday, but I know that Danios are hardy and assumed that if I kept and eye on levels and changed water as needed everything would be good. People cycle with Danios all the time. Obviously the NitrItes are spiking WAY more than would be expected on a normal cycle, so this has become majorly problematic.
Unfortunately removing the tabs isn't really an option, I'm sure they're dissolved by now and I don't know exactly where I put them. I can't really move the fish either, this is my first and only tank. They at least look well enough, so I think the big changes and Prime are at doing somewhat of a job to help them. I'll stop dosing macros, maybe that will encourage the plants to use more of the excess nutrients.
My last effort to save the tank is that I ordered two of the Active Filters - http://www.angelsplus.com/FiltersSpongeActive.htm
. I read amazing reviews from people on other forums saying that they completely jumpstarted their cycle in a couple days. They should be here on Thursday.
If all of that fails, I guess I'm gonna have to replace the substrate and start from scratch. Here's hoping it doesn't come to that!
Thanks for the help, and if you have any other thoughts I'd definitely appreciate.