I started using some apple cider vinegar in my pets water and adding brewers yeast to their diets (3 dogs and 3 cats) It took a month or so, during which I had them on Advantage, but didn't have to reapply any chemicals.
I just put about 2 tbs apple cider vinegar into a 4 gallon water reservoir.
If you do this, make sure all your animals will drink it. Don't know if some sensitive noses might not like the apple cider vinegar smell. I don't have a problem with mine.
