Hi Jesi. I'd suggest getting your own test kit, and monitoring your tank on a regular basis. 10 % water changes every week are a must also. Cartridge replacement type filters such as the Whisper line have the big drawback of losing their biological filtration abilities with every cartridge change. I've switched over to using the Aquaclear filter line, because of that flaw. You can make some modifications to the Whispers, so that there is extra media in there that can be salvaged while the cartridges are being replaced. Or better still, just rinse the cartridge off in the siphoned out water from the water changes, and re-use them. I do note, that in the last few years, the bio bag replacements have really gone down in quality, and fall apart much faster than they used to. Don't be discouraged, and keep learning, we all suffered losses in the early years.