Nitrite testing

[Blinky]

What if the nitrate level is ridiculously high, but the nitrite levels are moderate but steady?

How long has the tank been up and running? It's unusual for an established tank to have nitrites unless it's overstocked, which obviously isn't the case.
If you've got only 5 cardinals in a 25g tank and you've got very high nitrate and some nitrite, the first thing I think of is you could be either over-cleaning your filter media (killing off some of the beneficial bacteria), or you're not doing enough water changes.
I'd start doing 50% water changes daily to get the levels down to 0 nitrates and <25 nitrates, then weekly after that.

 

[happychem]

NO2 means that the cycle is not complete. You can still have really high NO3 and have NO2 in a tank that's partly cycled but not finished cycling if water changes are not being done (or being done insufficiently)

Dave, a product doesn't need to contain bacteria to convert NH3->NO2
->NO3, some products simply contain the enzymes that do the work. The bacteria produce the enzymes, they purify and bottle. While these may do exactly what they promise, they're worse than nothing because they remove the food source from the bacterial colonies. Also, while enzymes aren't just a one shot deal, after cycling through a few reactions, they tend to denature, i.e. fall apart and stop working.

 

[daveedka]

Dave, a product doesn't need to contain bacteria to convert NH3->NO2

Thanks for the clarification happy, I was assuming a lot with my reply, and probably shouldn't have.
Dave