my boy, also 6 months, has decreased his fluid intake because he's increased his solid intake. when he wakes in the morning he gets a short breastfeed as a snack... then about an hour later he gets some solid(more and more everyday!) and to top that off when he's finished, he gets a bottle.
that usually does him until around 11-12. then he gets some solid lunch and again another bottle to top him up.
he has a bottle again around 3 or 4 and dinner aroud 6pm. for dinner tonight he had: sweet potatoes, carrots, a very little bit of lamb(first time.... didn't like it at all!), some yoghurt, and bananas with blueberries. he had a little juice. then at 7:45 before bed he had another bottle.
he's started waking at night for another bottle(he has not done this since he was 13 weeks). i think that he's going through a growth spurt and needs the extra energy. i've tried giving him more to drink before bed, but he doesn't want it then.
i guess what i'm trying to say is... maybe your child needs more than just milk now?