Don't use the Grow for flowering. You'll have to switch to the floranova bloom. I've also heard that the Flora nova Liquid KoolBloom is a good bloom booster. Once you mix the nutes with water it shouldn't be too thick. Remember it's highly concentrated in the bottle. What I do is take syringe and suck in the right mount of nutes into the syringe (i.e. 1 ml, 2.5 ml or 5ml) and I squirt it into a 1 gallon jug of water. I shake it all up and it has the consistency of water.
You should note that the amount of nutes it tells you to use on the bottle is not for the plants that you are growing. The guy at the store I got mine from gave me a sheet to show me how much to use. Basically, the sheet says 1 ml per gal for seedlings, 2.5 ml per gallon for early growth and 5 ml for later growth. It also says you can put 7.5 ml/gallon for rapid growth - but the guy at the store said ignore that and don't put in more than 5ml per gallon ever. The other caveat is that while these nutes can be used for seedlings, many here recommend not using nutes for a few weeks. The cotyldon leaves are packed with all the nutes the plant needs in the first couple of weeks. Hope that helps!