I would dose 25mg/gal gal every day, so if your treatment tank is 20 gal then I would dose 500 mg. I think if you have fairly good lighting, the ciprofloxacin would breakdown with light so I assume that by the end of the day, you level is much lower if not all gone.
When my anemone is not doing well, I do 100% water change, I would still dose 25mg/gal. Right now I am treating two Gigantea in my HT, 20 gal high 50% fill. 1st day, last night, I change 100% of the water. Today, I will change only 50% of the water. They are doing much better. Last night I dosed 250 mg and will dose 250 mg today also. I have a 40 W flood LED 10,000K light on this tank. It is really bright with this LED.