Of course, I could be wrong, but I suspect that a lot, if not all, of the Nutrfin Cycle bacteria died because the flakes didn't decompose to ammonia quickly enough. You should've used janitor strength ammonia, from the hardware store (10% is okay), not the grocery store, the stuff without SURFACTAN and JUNK, added enough to bring the ammonia up to 3 ppm, maybe 4 ppm, and watch the bacteria feed by testing parameters. They should be able to bring those levels down to 0 within 24 hours, THAT'S A CYCLED TANK.
Some tap water can be legal to have as much as 5ppm ammonia. When dechlorinated, it leaves ammonia behind, because it was part of the chloramine, depends on your water company. I now use RO water to avoid all that ammonia, still have 0.25, even after adding a DI filter.
Are you new at this? A 6 gallon tank has very very little margin for error.
Yup, first it was the ammonia, then the nitrates, now the algae, what next?