When I switched from sugar to jaggery, my grains went from crumbly to chunky within a week. You can buy jaggery cheaply from Indian grocery stores. The cheapest are in heavy mounds which you'll need to grate first. I just use the powdered form for convenience.
Below is a strong jaggery solution and powder.
This soup skimmer is what I use and you can see it has a very fine mesh. (It's also great for straining coffee grains, making it an impromptu coffee filter). I bought this from a cheap homeware store.
I top up with cold water and add the water kefir grains. This is the finished product. The grains double easily within a few days when they are well fed and warm. From time to time I switch to refined sugar to steady their growth.
Check out the activity from using jaggery!
UPDATE: The jaggery I was using was terrible, it had too much sediment and produced a bitter drink. I ditched it and now I'm using palm sugar and white sugar. I will go back to jaggery but will try another brand.