A tip for dissolving reflux formula is after you have added the powder on top of the water put the top on, keep the bottle upright and roll it between your palms to let the powder fully settle into the water and then shake it! We had to do this with the formula my two were on, it also mixed better in cold water so it may be worth experimenting with the temp of the water in the bottles. We sterilised the bottles, put the once boiled water in, put the tops on and then kept them in the fridge until we needed them then we just added the powder and warmed.
It's not how you are *supposed* to make formula because the water isn't hot enough to kill any bacteria in the powder but they drank the formula straight away, it was never kept past the hour so we were happy that the risk was minimal and never had any issues.
Laura