High Water Level:
+ Larger volume of water, not so easily dirtied or fouled
+ Can be installed with most types of filter system
- Not all turtles can cope with high water level, 例如草龜
Low Water Level:
+ Most aquatic/semi-aquatic turtles can cope with low water level
- Only filter specifically designed for low water level can be used
- Less room for turtles to swim around
So, unless you have hatchlings or species not fit for swimming, I recommend mid to high water level.