How to make a good water deck?

I have a new 145 gallon tank for my red eared slider turtles, how can I make the water appropriate? ...and?

• I have a new 145 gallon tank for my red eared slider turtles, how can I make the water appropriate and healthy for my turtles? Also the water level has to go to the top of the tank in order for the water to get filtered properly. How can I make a sort of cage above the tank that will go completely around the tank? I need to make this upper cage like thing because since the water HAS to go to the top of the tank to filter, I can not put a basking area in without my turtles being able to crawl right off the side of the tank. Any ideas on how I can make a sort of "upper deck" to my tank? If you don't know, feel free to just answer my first question. :-)

• Answer:

  I think its a lot of work when you can buy a submersible pond filter which allows you not to fill your tank to the top and will still give you an area of land for their UV and basking. Building a cage around a tank that big will be messy and probably wet. both Supreme and Fluval make these submersible filters and they are not very expensive. there are pond filters also submersible that are bigger.