I placed a coarse sponge filter as the first layer from bottom, followed by another coarse sponge filter wrapped with dry wipe sheet, followed by the rest of the bio medias. Depending on your bio load, clogging can take place anytime from 2 weeks onwards. When my tank bioload is low, I have observed close to 2 mths of no-clogging usage. Most frequent I've experienced is once every 2 weeks.
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