Getting best out of my soap nuts

[GrendelsMum]

I've just tried a bunch of soap nuts in my washing machine, and they've done a reasonable job on my coloured clothes, but have left the whites slightly blotchy (I think they still have soap traces on them).

We have very hard water, so I used 7 soap-nut halves at 30%

Do I need to do whites and coloured clothes separately if I use the soap nuts, and add a teaspoon of bicarb to the white wash?

Are there any other tricks for soap nut use?

i tend not to use soapnuts on whites as they go greyish after a while - is that what the bicarb is supposed to prevent?

I'd aways do them seperately tho' to prevent the whites picking up any slight colour drift.