paint behavior

Question
My largest paint(Tripod) has become very inactive.  She lays around most of the day on a floating dock, not even on the basking rocks.  She rarely eats.  The young paint that I have, whom I believe is male (Chip), will frequently lay under the dock or hover partially on the dock with her.  When Tripod does come off the dock, Chip follows her very closely.  This has been going on for 4 days.  I am getting very concerned.  Do you think this is behavior caused by illness?  Could it be from getting ready to lay eggs or yet something else?  
***species - paint, habitat size - 150 gallon aquarium with 8 x 15 basking area, substrate - partialy flourite, partialy bare, humidity% - unknown, bask/ambient temps - unknown (50W light 8.5 inches from basking rock), whether you use thermometer or humidity gauge - do not use either, UVB lighting - yes both a daytime and night time light, type of UVB light (tube, coil, spot/flood) - spot, brand of UVB light - sunglo, vet history - none, all food offered - zoo med aquatic turtle food, dried shrimp, feeding schedule - morning and evening, supplements and schedule - none, last time ate - 3 days, when and how water is given - no additional water other than the tank (water is clear and filtered with a 4 stage canister filter), when last defecated - unknown, captive bred or wild caught - wild caught, was injured and missing a leg, she adjusted well and have had her now for 3 years, shed recently - no, other animals living in same terrarium - red ear slider, yellow belly slider, 2 paint hatchlings, 1 juvenile paint (believe to be male), some snails and a goldfish.  The paint in question, the 2 sliders and the fish have lived together for over 3 years.  The younger paint has been with them for a year.  The hatchlings have been with them from 2 months.
I appreciate any advice and insight you can give.  I have been unsuccessful in finding the information I am seeking anywhere else.  Thank you.

Answer
I'm unsure why you are using flourite here. Do you have live plants?

I need specifics on the UVB lamp. You stated under UVB lighting "yes both a daytime and night time light". Does this mean you are using a UVB light at night? "Daytime" lamp does not = UVB lamp. Under the question of basking/ambient temp you stated "50W light". I need all the lighting detailed in an orderly manner, from brand and model, to wattage and type. You also need a thermometer for the water, and one at the basking area. That's turtle keeping 101. Nobody is going to be able to tell you anything if you can't even give a temperature.

What is the construction of the basking area? Is it simply rocks?
How big is this turtle?

So, if I read this right, you have 6 turtles of varying species, in various stages of growth in the same aquarium...and all wild caught?