Well first of all, they shouldn't be leaking through! I have a number of Alva pocket diapers and I really like them. Is the insert saturated when they leak?
I use Kirkland (Costco's brand) liquid detergent in the free & clear version, my DD is 33 months old and that's what we've been using the whole time. Part of the thing with detergents is that if you have hard water and/or a front-loading washer you are more likely to have issues no matter your detergent. Otherwise things are more flexible and you'll find people using all different detergents with success.
One big thing is to avoid fabric softener and dryer sheets. They really prevent synthetic fibres from absorbing.