Taking a still wine and making it sparkling can be a bit tricky on
occasion. The carbonation changes a lot of things -- you might want to
try a few test bottles before you do the whole batch. Generally, the
wines used to make champagne tend to be a bit lower in body and a bit
higher in acidity than would be normal in still wines. I haven't made
that kit (either still or sparkling), so I can't guarantee the results,
but I'd suggest doing a bottle or two plain (no additions), then adding
1 to 2 g/l (0.1% to 0.2%) acid to a couple of test bottles, and compare
them. If the high-acid samples taste a lot better, try another sample
with 3 to 4 g/l additional acid. With a little experimentation, you
should find a level that works well for this kit and your tastes.

Doug