algae

i cleaned this out just a couple hours ago but just now i noticed little green pieces in the water. is it just them regurgitating into it or is that algae?

I am changing water in the bottles every couple of days and cleaning them with a bottle brush and the spouts with cotton buds once a week to help stop the build up of algae. I have the bottles in covers but it still doesn't stop the bottom (where the spout is) or the spout from getting...