Getmel...you can use water from the tap, but you need to make sure that your water purefication company doesn't use a chemical called chloromine. If it does you need to get something from a pet store to nuetralize this chemical. If they are only using chlorine, you will be fine with leaving your water set out for 24 hrs, and the chlorine will evaporate. This still leaves you with your original question though about the pH. You can use water from whatever source you have for the best water, but, you will want to get a pH adjuster (pH up and pH down) from either a pet store, or a hydro store. I always test pH of any solution before adding it to my plants. It is a good idea to check the run-off that comes out of the drainage holes to. This will tell you where to adjust the solution before putting it in next time.
Say you water with a pH of 6.5, but the run-off tests at 6.0 after running through your soil. You will want to make a note of this so that the next time you feed or water you can adjust the pH a little on the high side to get it where you want it in your soil. so if the run-off was 6.0, you will want to adjust the next batch to say 7.0 in the hopes that the run-off will raise to say 6.3, or 6.5. You don't want to overdue it though. say it is 5.5, you don't want to give the next batch at 8.0...you want to keep it under say 7.5, and make gradual adjustments.
Hope this helps ya!
