Hi,
My practice is using the Alpron solution but the company that makes alpron also makes DUWL dipside tests and Biofilm Removal kits for flushing the waterlines. We do a full biofilm removal once a year and do DUWL testing every 3/12.
The dipslides that you use from QWS are exposed to water from DUWL then left in storage for a few days at room temp then the results come up on the dipslide and you can send away for a certificate of compliance once you have done the initial test but for this you dont need to send away the dipslide you just complete a self decleration form and send to QWS this should be free if you have bought an alpron / bio film removal kit and they send you a recording sheet for the next 12 months so that you can document DUWL checks yourself. PM me if you have any further questions here is the web link:
www.qwsonline.co.uk/