red-eared slider

Question
I have a red-eared slider in a 30 gallon tank. I've had him for almost 4 years. He is now roughly the size of a playing card. I am interested in adding another turtle to the tank and I would like to know if this would be ok. If so, I would like to know if the second turtle would have to be a certain size. The turtles at any pet stores I've looked at are much smaller than he is, and not always the same kind. If you could give me any insight that would be great. Thank you!

Answer
Hello Chelsea,
At 4 yrs old he should be larger than a playing card. Can you tell me about your set up and lights and heat?
If you are looking to add another turtle, they will need a much larger set up to accomidate the territorial disputes and issues that can occur. Also please adopt from a rescue instead of a store because when you buy one from the store the pet store buys more causing supply and demand to increase. Then we can not get help in the rescues to stop the over breeding and we get overwelmed with rescues. Usually if you can show proper care, water turtles are free through a rescue.