guppy question

[Cap'n]

If your going the airstone route you could stick a bit of foam over the end and use that for your biological filter. That way you can change the carbon without starting a new cycle. I agree that is the problem, and I also agree that you should switch filters. On a 5g you can easily fit an aquaclear or similar. Go all out and get something with a biowheel, you won't be disappointed.