Your tank is uncycled and the ammonia is probably rising. Yesterdays test results don't mean much today. Do a large water change and the fish should perk up for a bit, until the ammonia starts to rise again.
So even adding the old filter, running both the new and old, it isn't giving the jump start it needs? How much longer do you think it will take? I mean as filthy as the old filter was, I really thought it would give the new tank the boost it needed to keep things sustainable for the fish to acclimate to the new environment. Also, this is actually day 8 and not 6. I started last Wednesday, it is Thursday now.