I've read several post regarding growing (extra) algae for oto's. So I'm giving it a try but not too sure I've got this right. I've placed some smooth river rocks in a glass bowl with water from tank (also swished the filter around in the water to help the process). The bowl is sitting in a sunny window for about a week now and so far I don't see any algae growing. The rocks do have a little slimy film on them but that’s it. We have had a couple of overcast days which the bowl did not get direct sunlight... Am I missing some part of the process? Does it take longer than a week? Thanks for your help!!