If what you mean is that the water flows over the top of the blue filter pad, that's normal. Once it is saturated, the water will still flow through the filter, but it will give the appearance of "not working", but it is.
I have a few of the 2gal, a 3gal, and the 6 gal systems. This is the way it works. More water is actually going "under/through" the filter than what appears to be on top. Dont worry, it is working just fine.
When you get a thin covering of brown "goo", dont rush to change the filter. That stuff is actually beneficial bacteria. Once it gets thick, then change the filter. You can actually rinse it off in the sink and reuse it. I only do it once per filter, but it can give you an extra 2-3 weeks out of it, depending on how many fish you have.
One way to know the filter is working, look at the water. As long as it's clean and clear, it's fine. Even after the brown "goo" shows up on the filter pad. As long as the water is still clear, dont worry.
And dont change or clean the biowheel. After awhile (1 year for me), you can rinse it off under the sink, but dont clean it. Even if it is spinning alittle slow. The faster the spin does NOT mean the better it works. Only when it gets to heavy from the brown "goo" and spins "off balance" do you need to rinse it. But dont scrub it off, just rinse under cool water.
