Our poor goldfish are going through some tough times right now as we wait for the nitrogen cycle to take over in our new aquarium. Having lost Daisy I early on, yesterday I had to euthanize Katharine (died 5/29/07), as the ammonia levels finally managed to take their toll on her and do her in. Being the cowards that we are, we again decided to replace the fish rather than sit down with Baby Exile and watch the Very Special ™ Harold and the Purple Crayon episode where Harold loses his pet goldfish Goldie. Fortunately there was a fish at the local pet store which looked almost exactly like our dear departed Katharine #1, and even better the clerk offered to give us an extra bag of tank water so as to help facilitate the growth of good bacteria to help kick-start the cycling process and prevent the other fish from suffering a similar fate.
So we introduced Katharine II (Baby Exile is either none the wiser or too wise to go down that particular rabbit hole) and all of the fish seem quite lively once more, but today I went to test the water and was shocked to find that the ammonia levels were 8 parts per million - twice the level that had killed off the first Katharine - even after having effected an almost 50% water change yesterday. The weird thing, however, was that even though the levels were so high the fish were more active and healthy-looking than we've seen them in days, so what gives?
Well upon testing the water's pH I discovered that it had dropped from around 7.4 to 6.4, making the water significantly more acid. While this can be a stressor for goldfish, it has the interesting side effect of neutralizing the toxicity of ammonia, especially when the temperature in the aquarium is on the moderate to low side, as the acidic water causes the ammonia to bind into ammonium, which is much less dangerous to fish. I found a great chart that shows the interrelationship of ammonia levels, pH, and temperature - it turns out that with a pH of 6.4 even an ammonia level of 8 ppm is safer than a 7.4 pH tank with 2 or even 4 part per million of ammonia!
So now the trick is keeping the water from getting too acidic while we ride out the cycling process and the tank's resident bacteria start converting ammonia to nitrites (and then the nitrites to much less harmless nitrates). Funny, nobody told us that we'd have to get PhD's in chemistry in order to raise a handful of goldfish! But it's a fascinating process nonetheless. Here's to hoping our current occupants will make it through the learning curve!