I'd just like to point out that bigger tanks do not need 100% monthly. It wouldn't interrupt the cycle unless everything dried out and then your BB dies but 100% monthly is not needed. 12 gallons each week will suffice just good enough! It's about 60% anyway and that's more than I'd do
But a full filter cleaning each month would help.
As for the girl, if poop looks normal then it's not internal parasites. It does look like she's got pop-eye going on and she can stay in the ES solution. How much ES are you using dancer? 1 teaspoon per gallon? You can use the 1 teaspoon per gallon while you use Kanaplex, it's not that stressful on them and it will both help but she does need an antibiotic for sure.