Welcome to Turtle Island
Robert W. Bly, founder, AquariumDetective.com
When I was a child, small turtles were popular pets - and seldom cared for properly.
Typically a child would be given a shallow plastic turtle habitat with two small green turtles. The plastic container held about an inch of water for the turtles to wallow around in, but it was not deep enough for swimming.
In the middle of this plastic habitat was a raised plastic bump with a little plastic palm tree sticking out of it. The turtles would climb out of the water and spend time sitting on the plastic bump, which we thought of as "turtle island."
Perhaps the manufacturer of the turtle habitat provided this tiny island because turtles like to sun their shells. But the palm tree blocked out most of the sun's healthful rays.
With no filtration and so little volume, the water in the plastic habitat would foul quickly. Children neglected it, so the little turtles got sick. Their shells softened, and they soon died.
When I got this turtle kit as a gift, I transferred them from the plastic habit, which I threw in the trash, to a clean 10-gallon aquarium with a filter, aerator, and light - an environment few of these green turtles were lucky enough to inhabit, in those days.
I filled the tank only half-way to the top with water. I thoroughly cleaned a couple of bricks and put them into the tank so the turtles would have an island to climb on.
The turtles spent part of the time swimming throughout the tank, after which they would climb out on to the brick and "sun" themselves under the basking lamp. They doubled in size, the shells got darker in color and harder.
Years later I got a 40-gallon tank with 3 turtles for my older son. He liked them but wasn't interested enough to maintain the tank, so the task fell to me.
Instead of bricks, I bought two bridge-like structures with steps on either side leading up to the horizontal surface. The steps made the bridge easier to mount than the bricks had been.
At the suggestion of the fish store owner, we put half a dozen small feeder goldfish into the tank, giving the turtles the option of live food. But the turtles ignored the feeder fish, and the goldfish rapidly began to grow, one getting almost as big as the turtles. He liked to lurk ominously under the bridges, and we named him Moby Dick.
With a strong basking light, you risk overgrowth of algae in your turtle tank, and our tank suffered from it. The heavy algae made cleaning a difficult, time-consuming, and somewhat disgusting task - algae is not fun to handle or scrape.
The algae would quickly turn the water from crystal clear to green-tinted and then, after a week or two, to almost pea soup thickness. Again, disgusting.
The most common problems with the pet turtles I have kept were eye infections and soft shell. Your fish store can sell you the eye medicine, a few drops of which you squeeze directly into the infected eye each day - not terribly difficult, and it works.
To combat soft shell, the turtles need long exposure of their shells to ultraviolet rays. That means either natural sunlight or a basking light with a UV bulb.
If you have young children, keep the turtle tank out of their reach and warn them against handling the turtles. Unknown to me when I was a child, when I was not home my kid sister and her friends would take the turtles out of the tank, spin them on a game-board spinner, and then watch them wander, dazed and confused, across the basement floor.
After you handle the turtles or the turtle-tank water, thoroughly wash your hands. Some turtles may carry salmonella, a dangerous bacteria that can make you pretty ill.