This is why I recommended super strong filter for Nezu. They fowl water very quickly.

Firstly, RES (your green turtle) love to bask. I use the word LOVE because they really love it. I suggest you make a space for them to do so. If you don't let them bask their shell formation will not be as nice.

Anyhow, you can try a filter. The common filter I used to use can only last 3 days before the water stank again. I took another approach. I fed them outside their living area. I used a slightly shallower big bucket, fill with water till their shoulder level, and fed them. Wait a while for them to eat finish and poo, then put them back in their living tank. This way, their water can last a little over one week.

Man... if you suck at keeping green turtles you think you can keep a ST? hehe, completely wrong ==. I have 3 res about 8 inches. They have been with me since i was 5 years old. Now im 13 their still healthy @_@.

The pics says it all your RES is indeed a Male !!!
As you also mention your RES as a he ( I mention in previous post that your RES has a high possibility of being a MALE ) - Dont be so stupid as to go trim his nails

They are supposed to be long to
- " stratch " the female's face to arouse her
- Hold on to female while trying to mate

Thats chelonian first instinct to hide when released !! Thgus going to hide in shady place is normal !!!

Never measured my RES. But here they are  . I think my RES are all bigger then 6 or 7 inches hehe. My box and my map too. They're shells haven't really been cleaned in awhile. So you can't see their shell markings hehe. (off topic) King you play WoW? just curious. private or official?

I think only 'SOHAI' who dont know take care of stars. I was kept ST for almost 10 years before. Dont face any major problem at all 
But now i allready retired & gave away all the star to other people