Flatworm Exit not working

[R7-12]

Hey everybody,

Looking for advice.

I have a 48x20x18" tank that holds about 55-60 gallons (after rock, sand etc.) with a 75 gallon sump with about about 30 gallons. About a month ago I noticed a few flatworms on the front glass. I treated the tank as per instructions (based on 80-90 gallons total), after an hour I added another 50% dose, made sure I had high flow by adding an extra Tunze nanostream, and it appeared to work. Within a few days I noticed one or two flatworms on the glass again!

About ten days later there were a few more so I treated the tank for the second time just as I had the first time. Same result. Two weeks later I treated for a third time but used a bit more Exit than the instructions suggest, waited 2 hours before using carbon and doing a water change. Again it appeared to work until the next day when I noticed one or two survivors on the glass again!

Not sure what is going on or what I might be doing wrong (am I under-dosing), but its becoming more expensive to deal with, not to mention frustrating as well.

Has anyone had this happen to them before? Has anyone double-dosed successfully with Exit?

Any suggestions/help would be much appreciated.

Thanks,
R7-12