I completed a 30% water change last night. Which worked well, since I used the gravel vac to save another 4 fry from a 9 fry drop (the other 5 I had scopped up in the a.m.)

I also washed the hood. I don't have any baking soda here, so I just used water and a deliagted scrub brush. But the hood wasn't smelly or mouldy at all. Good idea to do it anyway.

Then the filter, the floos was replaced again, and the whole unit was thoroughly rinsed, along with the carbon.

Tonight, no smell. The Nitrite level is a wee bit higher than right after the water change last night, the Nitrate remains the same.

So, was it a combination of both, the little "air pocket" and a needed water change? Or was it the water change itself?

I read on another site that suggested you don't need test kits to tell if the water quality is deteriorating. They were saying that if the water doesn't look or smell good, it's time to get at the water changes. Although simplistic (same for the rest of the site), to a degree that logic makes sense. But, I prefer not to wait until that point, I still use my test kits to tell me if there is a potential problem on the horizon... BEFORE it's a disaster.

Looks like I will be changing water twice a week in that tank until that biological cycle is properly established.

:)