While you may like the look of the stones as a basking area, it is not extremely in your turtles well being to use this. You are taking up a lot of valuable swimming space that they need. Also, should the stones shift over time, you could find an injured or dead turtle if they become trapped. Either build an above water basking area or buy one that will float with the water level. This way your turtles have the joy of all the water they need to swim in and live in.
The smaller rocks being used as substrate need to be disposed of as well. It is not recommended to use small rocks/gravel as substrate for turtle due to the fact that they will ingest them. If they become impacted it can lead to surgery or death from starvation. Usually turtle owners use a few river rocks for the turtles to push around but that are much larger than the turtles head so they will not be eaten. Also, having substrate in the bottom contributes to poorer water quality.
There's only one light in the pic (heat?). Do you have a UVB bulb as well? Both are needed over the basking area for turtles health and well being.
With a few tweaks and changes this will be a very nice home for your guys. I love the stand, I can't believe it was made. Great job.
