I would drip acclimate for 30 mins. I have seen fish gasp at the top going from a non-CO2 tank (.99 cent neons) to a CO2 tank. In thie case the CO2 tank was at least 30 ppm. The other tank ambient CO2 levels. Plus tap can vary. The KH from my tap varies between 2-6KH, and a large difference in KH is likely to stress fish.