Is there any reason you want to have two DNS servers? I would just disable the dhcp in the ISP router and let the pihole do the dhcp serving. This way your network is ad free as it get’s the pihole DNS by default. You then could set any device to the ISP router DNS manually. Just saves a lot of hassle, space, electricity and headaches when something goes wrong.
He thanks, finally rid of userbenchmark.com results.