Leave them be. You do not need to do any water change at this point.
Yes, making a mess is one of the downsides of using fish food for fishless cycling. Make sure your aquarium do not get a lot of light. It is the best to keep it in the dark. Otherwise all the extra nutrients (ammonia, phosphate, etc.) will cause an algae boom even before you add the fish.
Your PH is not acidic yet. Wait until the PH crashes to 5~6 before there is the need for partial water change to restore the water buffer and PH.
If you have the test kit for water hardness, you might as well get a reading of it. It is always good to know the general hardness of the tap water in your area. So you have a good idea on how easy your water PH will crash. The harder the water is, the more dissolved minerals there are, the more buffer the water has against PH crash. As for the fish, most of them will be able to get used to the new water hardness if you give them time to adapt before let them into your aquarium.
