I suggest making these improvements:
Poliwrath-I would get rid of whirlpool and hydro pump on Poliwrath. Neither move is reliable enough to be effective, and there's no point in having two water type moves. I would give him waterfall STAB. Being physical, it will do more damage. Earthquake would be good if you want to cover his electric weakness.
Slowking-Throw out water gun.
Feraligatr-There's no point in having 3 water moves. Dragon dance or swords dance would be perfect to boost up his stats. Earthquake could be good on him as well. for a STAB, give him either waterfall or aqua tail. Crunch or shadow claw can give more coverage, aerial ace too.
Kingdra-too many water moves. and the moves can be too weak.
In short, many of your pokemon have too many of the same type of moves, so you need to diversify your team.
Poliwrath-Waterfall, Ice punch, Submission, Earthquake
Feraligatr-Dragon Dance (or swords dance), Aqua tail (or waterfall), Crunch, Brick Break or aerial ace. (covers more types.)
Kingdra-Dragon Pulse, signal beam, Dragon Dance, Flash Cannon (flash cannon is unexpected on Kingdra)
Blastoise-Toxic, protect, Waterfall, rain dance
Slowking-Psychic, Light screen, Thunder wave, Surf
OR: for Slowking, you can make him a sweeper since lots of your team is pretty slow with this:
Trick Room, Nasty plot, Psychic, Surf.
Gyrados-Earthquake, Waterfall, Stone Edge, Dragon Dance.
The key to a monotype team is to make a diverse team. With these movesets I suggested, You can cover just about any type. Change this to your liking. Make sure to throw in a grass type or electric type move to deal with other water types.