While a pH og 6 is quite low, it should be fine (even favourable) for dwarf gouramies and you certainly shouldn^t attempt to change it as fluctuations in pH are gar more deadly than a pH that isn't 'perfect'. Changes in pH can be especialy stressful and, therefore, dangerous, for gouramies (as opposed to many other fish) - all the more the case with dwarfs as they are particularly prone to disease brought on by stress.