Hi Luqman, I have been to Durgam Cehruvu and I dont think there are big carps in that lake and moreover the water is contaminated with sewage, so if you catch any fish do not eat.
Catching eels is fun, I mostly caught them near the water fall, in the rocks. My biggest one was over half a meter. They usually bite on a big ball of worms.
Did you try that little lake around Gachi Bowli, there are lots of Carps and Snakeheads.
If you know any good locations around Hyderabad within the 50-60 Kms, please let me know. Or maybe we could go together sometime, what say?