TTM and Prophylactic Treatment

[lg2725]

A few weeks ago on a Sunday I picked up 2 Bangaii Cardinalfish and gave them a formalin bath in a 5 gallon bucket with an airstone for 45 minutes after acclimating them to the temp. Neither showed any sign of stress. I removed them and put them into 10G tank #1 for QT right after. I tried feeding them but neither wanted to eat. On Monday I tried feeding again and still to no avail. I was setting up 10G tank #2 for TTM (RODI water was ready but no salt in it yet) when I had an ammonia spike in #1 with the fish. Ammonia badge showed 0 but I tested with Red Sea Kit and it was there. In a rush I got the salinity and temp to match tank 1 and moved them over and dosed with Prazipro. There seemed to still be some salt floating in the tank but salinity stayed the same as I used a calibrated refractometer. Still the fish would not eat neither the pellets or Frozen Fish Frenzy. On Tuesday the larger of the 2 seemed almost catatonic for periods then swim about when he got in the bubbler stream. Wednesday I went to work and although neither ate, they both seemed fine. 4 hours later I came home from a meeting and both were dead.
I now have 2 black and white Osc. clownfish but have not done the Formaline or Prazipro. Both are eating and very vibrant. I am petrified to lose these fish. These have been our 1st fish purchases. I have a new tank with inverts and some corals in it that I will be running fallow for 72 days. Any thoughts to what I could have done wrong and about not using Formaline or Prazipro for these 2 clowns?
I know this was long but I felt you needed all of the steps that I went through.
happy Reefing. Thanks All.