water kefir or Tibicos grains

I've been using them for maybe a month now, and I didn't use very good dried fruit (perservatives ) well my brew started to get really sulfurous. I switched to healthier ingrediants and now it has this umm not alcoholic but a nasty organic taste, maybe formaldehyde could describe it.

Does any one have any information about how to rejuvenate or possibly how to diagnose kefir health?

So far,

I have switched to lighter sugars (molassas free)
using organic raisins
always used filtered water (change filter regularly)
do not let metal contact the kefir
brew it for 2 days max (may drop this down to 1 day)

 

well they're far healthier now. The kefir water is fresh and fruity. If anyone in nz would like some , i have a heap that have been dried out that i can post