How long have you had it? I have had them for about 4 months
What is the water temperature? 78 degrees now. I just got a water heater.
Did you use a thermometer? The water heater says it is preset at 78
Are you using a water heater? Yes
How much water is in there? Enough that the turtles can swim without being out of the water or touching the bottom, but there are places in the habitat to take a rest.
Are you using a water conditioner? Yes.
Are you using any filtration? Yes.
What is the basking temperature? 80
Is there a basking light? Yes
Is there a basking platform that is easy to climb on? Yes
What kind is it or what is it made out of? A basking light. That's what the box was labeled, at least.
Is there a UVB light? Yes, I just got one last week, but I think I may have been slightly late on that, hence the recent floating?
What have you been trying to feed them? Yes. I have "Turtle Treats" (the really like those.. they wont really eat anything else), Turtle Sticks, Aquatic Turtle food and some little red pellets that they came with when I bought them in Chinatown LA ..go ahead, judge me
When was the last time your turtle ate? Yesterday
How big is the tank/pond/enclosure? I am unsure of the gallon size, but I know since they are so small, it must be plenty big. There's enough room to have a basking area on one side and then on the opposite side is the filter and another resting spot.
Is the tank near a window? Slightly.. a draft may be an issue
Is the tank in a room with a lot of activity? Yes. It's in the front room.. by the front door.. again, drafts may be an issue
Have you read the Basic Care section? Yes
Have you searched the forums for similar situations? Yes
Is there any other unusual activity/symptoms? I am assuming they were near the same age, but one has grown might quicker than the other. The smaller one has some spots on the shell (were there when I bought them) and the bigger one's shell looks fine. I will try and take pictures when I get home, but we're in the middle of moving, so it may be a little before I can.
The bigger one starting floating on the right side late last week. By now, his whole back side is floating and he's been wedging himself (carefully) under the backing area in order to stay put.

