First, we highly recommend you purchase a new environment for the turtle. Half a gallon is 19.5 gallons too little for a hatchling turtle, and if he/she is larger than that, even smaller! But in regards to your question, you would use about 1/8 of a teaspoon.
Turtles require large tanks they can swim and dive in, and the capability to sleep under large rocks or logs. They also require weekly partial water changes, plenty of filtration, a UVB lamp and a basking lamp. Water temperatures should be around 70-75 degrees and the basking area should have an air temperature around 90-95 degrees.
Please let us know if we can be of further help!
Date published: 2018-02-01