I want to get on my soapbox! 'PRETTY TURTLE' IS NOT A STREPTOCARPUS. There we go - I said it. It may be sold as a Streptocarpus at garden centres and online, but it is not! It is a Primulina and is in the same family as Streps and Gloxinias (the Gesneriad family).
It's a piece of marketing I really can't understand. Can you imagine the meeting...
'Primulina is difficult to pronounce'
'I know, let's call it a Streptocarpus instead - that's dead easy to say'
'Brilliant!'
It's a beautiful genus and I highly recommend having a go at growing Primulinas (but they are not streptocarpus!)