tidal 75

Aqueon 40 breeder with glass lid. Comes with Seachem Tidal 55 and Tidal 75. Also comes with a Cobalt neo-therm 200 watt heater. Back panel is covered with black vinyl, not paint. Also comes with a black stand with a shelf. No cracks or leaks. Purchased a large tank and won't be using this one...

I’ve seen people say to run both at once, or use as much filter media as possible in the new filter. however, is this necessary and if so why? I replace my sponges often, just whenever they seem too dirty after a rinse. Is this not just like replacing the HOB altogether?