normally what i am doing is put new comer with the water in the bag into a pail/hospital tank first and slowly add in 1/3 of settled water into the pail/hospital tank. then 1 or 2 hrs later add in another 1/3 of settled water into it... repeating 3 to 4 time till the pH for the pail/hospital tank is almost same as settled water's pH. lastly, add the new comer into the settled tank will do...

hope this help...