Specific pet gel formulas are available from your veterinarian - NEVER use human formulas as they are toxic.
Blood levels of potassium (and other blood values) must be checked to determine the proper dosage and should be monitored regularly. Diet and supplement amounts need to be adjusted accordingly as your pet ages.
Work closely with your vet to avoid complications such as overdosage - this can be deadly as too much potassium will adversely affect cardiac function.