I would have filled the tank with water and added enough bleach to make the water feel slippery. The bleach will oxidize organics in the tank making them much easier to remove. I would have let it sit and then scrub well before draining and rinsing. Then I would have washed down with straight vinegar to remove hard water stains, and rinse. I would do the same with all hard parts of the filter. Bleach will ruin sponges, so I don't use it for that. Usually I will run the filter box and all hard plastic parts through the dishwasher, using detergent, because I am lazy and it does a great job.
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