You can try using those new type toothbrushes with ultra fine bristles, they can help reach into the narrower areas to scrub out more dirt and algae... just like for teeth.![]()
There is a limit to how much you can scrub out though, if you used all your effort and there are still some remnants of the algae in the silicone, then those are probably already grown too deep in to clean. So i guess you either have to change the tank or just live with it.
I have also experienced this before in my older tanks that have been in use for more than 3-4 years, but i do find that regular scrubbing with a toothbrush during tank maintenance (even if there are no visible algae yet) can help to delay the effect for a longer time.![]()
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