I believe it is always important to compare the water parameters (PH, GH, KH and temperature) at the beginning of the acclimation period. If the parameters are 'very, very close' than 30 minutes of acclimation might be OK. adding 25% of the tank water to the amount in the bag every 10 minutes (assuming there is not too much water in the bag). If the parameters are very different from the bag to the tank, then I would advise at least two hours, personally I acclimate for three hours or more adding only 10% every 15 minutes and emptying out half the water from the bag after an hour. I've actually acclimated fish for 4 hours before. The transporting of fish can be stressful to begin with, but too much change in ph and hardness can be devastating for some fish. Also, it is not advised to empty the bag of water into the fish tank, rather net the fish or pour the water into a net and throw the water out, just in case of any free swimming parasites or other contaminants. Better to be safe than sorry. NOTE: When introducing new fish to an established tank it is advised to quarantine them first for two to five weeks in a separate cycled tank. GOOD LUCK!