Need help cleaning clear retainers!?

I have these clear retainers for about 4 months now and its starting to turn ugly. There are unclear white stuff in my retainers. I brush my retainers everyday and occasionally use the sonic cleaner along with a tablet to clean my retainers. But the white stuff will not go away. Any suggestions on how to completely... show more I have these clear retainers for about 4 months now and its starting to turn ugly. There are unclear white stuff in my retainers. I brush my retainers everyday and occasionally use the sonic cleaner along with a tablet to clean my retainers. But the white stuff will not go away. Any suggestions on how to completely clean retainers?

* I think the white stuff may be plaque or some kind of chemical build up.
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