Fishy situation

I just *know* you've been dying to hear how our fish are faring.

Well, they seem happy enough, despite having to cope with the chemical toilet that masquerades as an early-life aquarium undergoing its first cycle. I just completed my third week of tests, and - as far as this novice can tell at any rate - things are progressing as expected.

A healthy aquarium contains several kinds of bacteria that convert the ammonia produced by the fish and the decomposition of left over food into nitrites and those nitrites into safer nitrates. In a stable tank, ammonia and nitrite levels should be almost undetectable, and nitrates gradually accumulating in the water through the bacterial activity are removed by doing partial water changes each week.

In a young aquarium, the bacteria haven't established colonies of sufficient size to deal with the chemicals, so levels gradually rise in the first couple of weeks. I've seen exactly this with my testing. Levels of ammonia peaked last week, but have now dropped off to the lowest number so far recorded (about 0.4ppm), whereas nitrite levels, which were relatively low last week, are now extremely high. This indicates we're almost exactly at the mid-point of the cycle, but because nitrite is especially dangerous to fish (it binds to haemoglobin and can leave them gasping for oxygen) I've done a 20% water change this week instead of the usual 10%.

By this time next week nitrite levels should be dropping and hopefully in a couple of weeks the aquarium will have fully cycled and we'll be able to add three more friends for Bee, Bop and Lulu to bring the cherry barb shoal up to full strength.