I'm running a 10 gl tank with a Aqueon Quiet Flow filter. It comes with a red light which supposedly flashes red when it's time to change the filter. Problem is that the light started flashing after about 3 weeks of the cartridge being inserted. I rinsed the cartridge and put it back. Still flashing. So I gave in and changed it, but not before I let the new cartridge being seeded by the old one. That was 3 days ago. I might have even crashed my cycle by changing the cartridge but what's done is done. Now 3 days later, with the new cartridge the light starts flashing again. I mean come on...what is going on ? Is that a legit warning or a gimmick to make people buy cartridges often?