By David A. Lass
Q. I'm 12 years old and a big fan of your column. I have a 16-gallon community aquariumwith Anacharis and eel grass plants. The fish include a female guppy, a black ghost (which I plan to move if it gets too big), a rasbora, a male platy and an algae-eating shrimp. The pH is 7.0, and the temperature is 78 degrees Fahrenheit. I was thinking about getting a pleco, a few more rasboras, a male and female guppy, and a female platy. Also, my dealer said that I could get some Corydoras catfish. However, books (and your magazine) say they need a lower pH. Are the fish I plan to get appropriate for my aquarium? Can the cories handle a pH of 7.0? If not, could I lower the pH without hurting the fish I have and those I am planning to get?
Don Lubben
A. Corydoras catfish are cute, easy to keep, adaptable and clean up uneaten fish food (but you still need to make sure they're getting enough to eat). Cory cats are what is called "crepuscular," which means that they are most active at dawn and dusk. You should always drop a little fish food in right before the lights go off for the day.
The three most common Corydoras that you will see in your local fish store are Corydoras aeneas, C. paleatus and an albino form of either of these two species. These fish are adaptable to a pH from 6.5 to 7.5, although in the wild they are found in waters that are more acidic, with a pH down to 6.2 or even lower. These three cories will have no problem adjusting to the pH range I've suggested.
The most common wild species (unlike the captive-raised species noted earlier) are C. julii, C. punctatus and C. melanistius. These three all look pretty much the same: black spots over a silver body.
The most important factor concerning pH is that the pH value of your aquarium water be consistent. A consistent pH that is somewhat outside the desired range is less of a problem than pH values that fluctuate. Fish do not react well to drastic and/or sudden changes in pH.
When you purchase cory cats from your local fish store, ask them to take a reading of the pH in the aquarium they came from. Compare this with the pH reading of the aquarium where you are going to introduce the cories. When you get your fish home, empty the bag into a small bowl or bucket. Then, every five minutes or so for a half hour, take a small cup of water from your aquarium, and put it into the bucket. Doing this in small amounts and over a period of time will slowly acclimatize the fish to your water conditions. When the pH in the bucket is very close to the pH in your aquarium, it is safe to net out the fish and put them into your aquarium.
The aquarium we are talking about is, of course (for every good FishKid), a quarantine aquarium. This is where you will keep the new introductions for two or three weeks to make sure they do not bring any disease into your show aquarium.
One final thing with cory cats: Please keep them in schools of at least three — five or more is even better. They don't all have to be the same species, as long as they are all Corydoras. In nature, they occur in huge shoals or schools, and will not feel secure if they are alone in an aquarium.