Well maybe they can come do tests on my animals water. I have kept rodents, guinea pigs and other animals that use the bottles- and I have always had the same problem. All our water is done regularly, and the bottles are washed to keep the algae away.
I believe the sunlight that our animals water has shine on it encourages algael growth no matter the water (I've used tap water, distilled water, spring water all in our watering system for the animals, and STILL the algae forms.)
We change water everyday, and still the algae forms. And what 'westhamsc' said is true of the algae,but essentially, if all you are doing is replacing one lot of tap water with another lot of tap water in the bottle WITHOUT washing it (getting rid of any 'algael' residue) then you will continue to have the problem no matter how many times a day you change the water.