Moving into my new house tomorrow and the fish tanks will be first on the list. Had a guy come to test the water for a water softener that will be put in but not till tues. The ph right now is 20 from what he said. I need to get this down to 7-8ph, have a 150 gal being my biggest. Fish are pretty hardy, how long do I wait after putting ph decreaser in the water till it's safe?