Having trouble trying to get your pH up? Safest way is to add crushed seashells to the system but this will take a long time to buffer . You will notice after a lot of rain has entered your system, that the pH has perhaps dropped dramatically. This sudden drop can be detrimental to your fish. To bring your pH up at a faster but safer rate, use Potassium Bicarbonate. You only need to dissolve a teaspoon into a bucket of tank water and tip it in your 1000lt fishtank. Check pH the next day and if it needs to be repeated, do so. Do not continue to add on the same day and remember to check before adding more. It can rise to quickly if this is done.