It may be a little late but here is a post about using FWE by Mark Peterson from WMAS. His recommendations are a little different than the directions on the product.
Fish are great Flatworm eaters if they are hungry enough. Besides the Six-line, other fish that eat flatworms are Yellow-tail Blue Damsels, Mandarins and some other wrasses, one especially good wrasse whose name I don't recall now, but I believe it starts with the letter M.
Show us your tank by posting a few pics. It could help us help you.
To get fish to eat things like Flatworms, it is sometimes necessary to stop the feeding. Let them go hungry and they will search for other food in the tank.
There is another medication, much cheaper than FW Exit. It is a pig medication called Levamisole.
When using any medication, we have found that it is better to utilize a sequence of increasingly larger doses. I have discussed this here on the MB many times regarding Flatworm Exit. Basically you start with a 10% dosage (1 drop FW Exit per 10 gallons) and see if the flatworms start to wiggle and move around. If they don't show signs of irritation in about 5-10 minutes, add another 10% dosage. When you see some flatworms releasing their hold and floating around the tank, wait 30-45 minutes and then add a bag of AC (Activated Carbon) in a place of good flow, typically this is near an intake or if you have a HOB filter use that. Don't use a so called "AC Reactor" That works too slowly.
The next day remove the AC and repeat the procedure above. This dosage will probably reach 50% before the remaining flatworms start to die. Repeat this each day until the dosage has reached 100-200% and no flatworms are left.
Don't forget to add the AC after the last, largest dosage.
There are two extremely important reasons for using Flatworm Exit according to this slow dosage procedure rather than the manufacturers directions.
1. ** Some tanks have so many flatworms, many of them hidden, that the full dosage overwhelms the tank with dead flatworms releasing lethal toxins into the water and even with major water changes, fish and coral may be lost. The slow dosing procedure puts NO fish or coral at risk of death.
2. The trouble and effort of siphoning flatworms and doing a massive water change is completely unnecessary with the slow dosing method.
Edited by Mark Peterson - February 25 2009 at 9:28am