A 40-gallon tank is not large enough for many types of turtles, including the red-eared slider. However, there are a few species of turtles that can thrive in a 40 gallon tank.
While there can certainly be exceptions, you should generally have 10 gallons of tank for every inch of your turtle’s length. Therefore, if you plan on having a 40 gallon tank, you should choose a turtle that doesn’t grow larger than 4-5 inches. If you have the proper habitat, a 40 gallon tank can be suitable for a 6 inch turtle.
If you haven’t bought a tank yet, you should check out this cheap 40 gallon tank. It only costs $110.
What Turtles Can Live in a 40 Gallon Tank?
The best turtles for a 40 gallon tank are Musk Turtles, Eastern Box Turtle, Mississippi Map Turtle, Reeve’s Turtle, Three Striped Mud Turtle, Texas Map Turtle, and the Razorback Musk Turtle.
1. Common Musk Turtle
Common Musk turtles are small turtles that range from 4-4.5 inches in size. They are common turtles that you can easily find in pet stores.
If you want to keep only one adult Musk Turtle, a 20-gallon tank is enough. But since you have a 40-gallon tank, you can also house a pair (keeping two male turtles of these species together are not recommended, though).
2. Eastern Box Turtle
Eastern Box Turtles are a great option if you prefer a turtle that doesn’t swim a lot. A big advantage of Eastern Box Turtles is that they require less maintenance since you don’t have to constantly maintain the water.
While an Eastern Box Turtle can certainly live in a 40 gallon tank, you should look for a tank that has more surface area on the bottom and less height.
While they can be shy, they are known for being one of the nicer species of turtles. If you do go with this turtle, make sure you get a powerful UVB light. You also want to make sure you get a lot of substrate since these turtle like to dig.
3. Mississippi Map Turtles
Mississippi Map Turtles are another great pet turtle. However, with a 40 gallon tank, you should only have a male. This is because while male Mississippi Map Turtles only grow to a length of 5 inches, females can grow up to 10 inches.
These turtles love to swim, so make sure they have enough water to do so. While it is still important to maintain clean water, they are a bit hardier than other species and can withstand tougher conditions.
If you are getting a baby, you should check out my article on what to feed a baby Mississippi Map Turtle.
4. Reeve’s Turtle
Reeve’s Turtles are one of the most beginner-friendly turtles with low maintenance requirements. They have great personalities; and are peaceful and active species.
Generally, for a single adult Reeve’s Turtle, at least a 30-gallon tank is good. So a 40-gallon tank is a nice start for keeping these pets. But a bigger tank, such as a 50 gallon turtle tank, is usually more acceptable.
5. Three Striped Mud Turtle
Three-striped turtles are one of the smallest and best turtles you can keep in your tank.
These turtles don’t need a huge tank. Even a 20-gallon tank is enough to house 2-3 adults of these species. If you want smaller than a 40 gallon tank, you should check out my guide on tanks for small turtles.
The three-striped turtles are mostly 3-5 inches and can live around 30-40 years. Their natural habitat includes Florida, Georgia, and some parts of Southern California.
The general rule for housing these turtles is to offer 10 gallons of water for every inch of the shell.
It is good to have a flat surface in the tank where they can come off the water and bask.
For creating basking areas, you can use cork bark, driftwood, smooth rocks, or any stable platform that offers a flat surface.
If you go with driftwood, make sure you properly prepare it before putting it in your aquarium.
6. Texas Map Turtle
Another turtle that can do well in a 40-gallon tank is the Texas Map Turtle. Ideally, a single Texas Map turtle needs at least a 30-gallon tank.
But a bigger tank is always preferable, like a 40-gallon or more, as that allows the turtle to have appropriate swimming space.
These turtles also do well in a community habitat with others like Musk, Mud, Cooter, and Painted Turtles.
7. Razorback Musk Turtle
The Razorback Musk Turtle originates from North America, and they are almost fully aquatic species. These turtles have a docile temperament, and their adult size can be up to 5-6 inches.
The Razorback Turtles are usually found in the Northern American states like Arkansas, Mississippi, Florida, Texas, Louisiana, and Oklahoma.
Generally, 20 gallons are enough to keep only one adult of these species. However, if you want to house a pair, it is good to have at least 30 gallons.
So, a 40 gallon tank setup is a good start for housing these species.
Although these turtles are mostly aquatic, they can sometimes look for land areas where they can bask. Hence, you can use a small rock to create their basking area.
The ideal basking temperature for these turtles is 82-90 °F, and the water temperature is 74-79°F.
A submersible aquarium heater can be helpful to maintain the water temperature. Also, you can have a good filter (preferably with a low water flow) to keep the water clean.