well... to start off, your turtle should NOT be growing at a rapid rate, and you should not be seeing it shedding often!Again, as most would agree, i really wish people would read up on their animals before buying them. your turtle should actually only grow 'about' an inch per year!
there could be 2 reasons your turtle is shedding, the first (and less likely) is that the water temperature is too high, i would say anything above 80 is too warm. the other (and more LIKELY) reason is because you are overfeeding your turtle which will probably lead to irreversible pyramiding of the shell and early death of your turtle. you should ONLY be feeding your turtle the size of protein (aka pellets) that would fit in his head per day (for first yearling turtles) and any turtles over a year or two old should only eat EVER OTHER day! the rest of the time you should be introducing your turtle to greens (dandelion leaves, collard greens, broccoli, lettuce (not iceburg), and any other fruits or vegetables that he/she will eat). you can feed as many greens as you would like, these will not cause the turtle to become overweight, they are more for nutrients. although, you should not feed your turtle the SAME greens everyday, they should have a varied diet for proper growth of their shell and body.
and please, if you did not know any of this, research your pets before you buy them. this way you won't cause harm to your animals!
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~ Evie 
Pets:
RIP 0.1.0 German Shepherd {Dusty}
0.1.0 German Shepherd/Collie mix {Shadoe}
0.0.2 RES turtles {Booger & Snot}
1.0.0 African Clawed Frog {Bingo}
0.0.2 Snail {Gary & Larry}