I can not see where it says you started with 1/4 FloraNova. The first page of this thread says "Nutes: House & Garden Aqua Flakes".
Root rot happens for 2 main reasons.
1) Root cells don't get enough oxygen, get mushy, and die
2) Root cells don't get a proper nutrient balance, get mushy, and die.
Rot then infects the weak roots, and the weak roots are blamed on the rot.
Yet everyone on RIU is chasing their tails trying to fix the issue with sterilization and magic teas, which I never used, and never had root rot.