Sorry, but I disagree. Even in a cycled tank (like the one my fish is in) will have small spikes up to .25 occasionally. .25 won't harm fish short-term. As I've said in other threads, if it's 0 while still cycling, there won't be enough for the BB to feed on. It's excessive to try to get an uncycled tank to read 0, and it might cause more stress. For instance, you'd have to do a 100% WC to actually get it to read zero. .25 is a good base level that it shouldn't get above.