Rejuvenating Water Kefir grains?

I had water kefir that I gave to a friend, she never used them (stored them in the refrig for about 6 months) and just gave them back to me. They looked good and smelled good so I put them in some water, lemon, apricots and sugar. I let them sit for abotu 30 hours and then strained, rinsed and redid the water, etc. The "juice" tastes very sweet, not like I remember, no tanginess or fermented taste. And the new batch doesn't even taste close to what I remember water kefir juice tasting like.

I like the fermented sweet/sour taste that my WK used to be, how do I get it back to that?

What is it supposed to taste like?

Any suggestions?

Thanks