Posted: Wed Mar 25, 2015 7:04 pm Re: cost of outdoor habitat
I agree with Steve about waiting for them to get larger. RES at the size of your turtles have a good chance of being attacked by a predator, as well as acquiring health problems from environmental fluctuations. Whether you have male/male, male/female, or even female/female, it's usually best to separate in the long run--which would require you to set up more than one outdoor enclosure. (Either that, or keep one inside while the other goes outside, and switch them off regularly). This year, I'm taking the latter approach.
That being said, if you really do want to go through with an outdoor setup, you might be able to use the enclosure you already have (am I right in assuming that it's a galvanized stock tank)? If you put the tub in an area on your patio with access to both unfiltered sunlight and some shade, all you have to do is find a protective top for it and you should be okay. As long as the temperatures are above 70F (preferably 75F and up), you don't need a heat lamp outside. Remember that water is usually a few degrees lower than the air, so you may need a water heater until the air reaches at least 80F (again, warm temperatures are a little more crucial in your case because you have such young/small RES).
Yes, you will still need filtration outdoors. You can buy a commercial pond filter, or build your own (there are lots of instructions online; I build barrel filters from plastic drums. Soda manufacturers and car washes frequently give them away).