There's so many posts on turtles here, I thought I'd make a post for them. Just a very basic guide, nothing too in-depth. I'm no expert. Sorry if there is one already.
Okay, so you just got a few free turtles from your lfs! They're only about an inch big and they're SOOO cute!
You stick them in a half full ten gallon with a Whisper filter.
Six months later your turtles are bigger... much bigger.
The water's all cloudy. What's going on?
Many people are surprised to find how large their turtles will get, how big of a tank they need, and how to properly care for them.
Species.
Knowing the type of turtle you have is very important in creating a suitable habitat. Here are some of the most common turtles:
Red Eared Slider.
This is one of the most common turtles, and a very hardy one to keep. Unfortunately they grow very large, up to about 12" in females.
They need large tanks and they MUST have a land area, they bask a lot.
Painted Turtles
There are four varieties of these turtles, but care is basically the same. Pictured is a Midland painted turtle which can grow to about 8 inches.
They are also extensive baskers.
Mississippi Map Turtle
The max size for this speices is 5" for males, 10" for females. They need lots of swimming and basking room
Common Musk Turtle
This is a very common species where I live. They get to about 5 inches and don't seem to bask very often. They are great swimmers, though.
Eastern Box Turtle
THESE TURTLES ARE NOT AQUATIC. Please do not drown them.
Basic Care Info
Generally turtles need much large tanks than expected. The 'rule' for selecting a turtle tank is 10 US gallons for every inch of turtle. So a turtle that is 5 inches long will need about 50 gallons of water. Not a half filled 55 gallon.
A full 50 gallons. 
This allows for waste dilution, and also more space for the turtle.
Speaking of waste dilution, what kind of filter do you have again?
Toss that whisper and get a real filter. Turtle waste is much bigger than your neons'! Many people will recommend a canister filter rated to two times your tank's full volume.
Another thing to consider when buying a turtle is land area.
All turtles NEED a land area, where they can get completely out of the water to dry off and bask. The turtle needs to be able to comfortably fit on the land area. It should be heated, but there should still be room to move to a cooler spot. There should also be a UVB light. UVB lights are meant to simulate the sun, which helps the turtles shell stay healthy. 
What kind of substrate have you got in there?
Gravel? Be careful! Turtles can choke on that. The best options are sand, bare bottom, or large pebbles.
Still missing something? What about a heater? No, room temperature isn't right.
The temperature varies form species to species, so make sure you look it up.
So now you've got your two musk turtles that are 5" in a 100 gallon tank, with a nice toasty log and clean, filtered water. Great! Well, not totally. They're still looking kinda thin... did you forget to feed them?
Most people just toss in some pellets and are done with it. That's not a good habit. You should watch your turtle eat everyday, to make sure it eats, your feeding the right amount, and that there's not other problems. Also, the diet should be varied. Brand name turtle pellets such as reptomin are good, but switch it up occasionally with some romaine lettuce, anarcharis, bloodworms, shrimp, or snails.
Hopefully you have a better understanding of how to take care of your pets now. Keep in mind there are many other things to consider than what is listed here. For example, maintenance. Don't forget that! Once you know what kind of turtle you have, do all the research you can to make sure your providing a proper home for it. Good luck.
Photos from Austin's turtle page.
Okay, so you just got a few free turtles from your lfs! They're only about an inch big and they're SOOO cute!
You stick them in a half full ten gallon with a Whisper filter. Six months later your turtles are bigger... much bigger.
The water's all cloudy. What's going on?Many people are surprised to find how large their turtles will get, how big of a tank they need, and how to properly care for them.
Species.
Knowing the type of turtle you have is very important in creating a suitable habitat. Here are some of the most common turtles:
Red Eared Slider.
This is one of the most common turtles, and a very hardy one to keep. Unfortunately they grow very large, up to about 12" in females.
They need large tanks and they MUST have a land area, they bask a lot.
Painted Turtles
There are four varieties of these turtles, but care is basically the same. Pictured is a Midland painted turtle which can grow to about 8 inches.
They are also extensive baskers.
Mississippi Map Turtle
The max size for this speices is 5" for males, 10" for females. They need lots of swimming and basking room
Common Musk Turtle
This is a very common species where I live. They get to about 5 inches and don't seem to bask very often. They are great swimmers, though.
Eastern Box Turtle
THESE TURTLES ARE NOT AQUATIC. Please do not drown them.
Basic Care Info
Generally turtles need much large tanks than expected. The 'rule' for selecting a turtle tank is 10 US gallons for every inch of turtle. So a turtle that is 5 inches long will need about 50 gallons of water. Not a half filled 55 gallon.
A full 50 gallons. This allows for waste dilution, and also more space for the turtle.Speaking of waste dilution, what kind of filter do you have again?
Toss that whisper and get a real filter. Turtle waste is much bigger than your neons'! Many people will recommend a canister filter rated to two times your tank's full volume. Another thing to consider when buying a turtle is land area.
All turtles NEED a land area, where they can get completely out of the water to dry off and bask. The turtle needs to be able to comfortably fit on the land area. It should be heated, but there should still be room to move to a cooler spot. There should also be a UVB light. UVB lights are meant to simulate the sun, which helps the turtles shell stay healthy. What kind of substrate have you got in there?
Gravel? Be careful! Turtles can choke on that. The best options are sand, bare bottom, or large pebbles. Still missing something? What about a heater? No, room temperature isn't right.
The temperature varies form species to species, so make sure you look it up. So now you've got your two musk turtles that are 5" in a 100 gallon tank, with a nice toasty log and clean, filtered water. Great! Well, not totally. They're still looking kinda thin... did you forget to feed them?
Most people just toss in some pellets and are done with it. That's not a good habit. You should watch your turtle eat everyday, to make sure it eats, your feeding the right amount, and that there's not other problems. Also, the diet should be varied. Brand name turtle pellets such as reptomin are good, but switch it up occasionally with some romaine lettuce, anarcharis, bloodworms, shrimp, or snails.
Hopefully you have a better understanding of how to take care of your pets now. Keep in mind there are many other things to consider than what is listed here. For example, maintenance. Don't forget that! Once you know what kind of turtle you have, do all the research you can to make sure your providing a proper home for it. Good luck.
Photos from Austin's turtle page.
