Ethernet fine, wifi dead slow or stopped untilrouter restart

[#1]

Hi all
I've a Thomson TG585 v8 and it's connected to my primary PC via Ethernet. This PC is always fine for speed and connectivity averaging around 16.5 Mbps d/l.
However, my wifi speeds gradually creep down and down until it's unusable and I have to restart the router. After a restart it's OK on wireless for a few days and then it creeps away again.
I have changed the DNS servers on the router to openDNS to help limit the kids' chance of accidentally finding something unpleasant but I'm at a loss to see how that would interfere with Wi-Fi speeds whilst leaving the Ethernet speeds untouched.
IT makes no difference where the Wi-Fi devices are; upstairs, two rooms away from the router or right next to it. They all stop working eventually.
Any ideas chaps?
Best regards
Andy

[#2]

Hi Andy,
The best place to start looking at this issue would be using a program such as inSSIDer: http://www.metageek.net/products/inssider/ to scan for other networks that may be sharing the same channels/set of channels and possibly interfering with your WiFi network. Following that try logging into the router's settings page: http://www.plus.net/support/broadband/hardware/thomson_wireless.shtml then try changing channel selection to "manual" and see if you get any improvement by using the different channels available. I believe the higher ones (6-11) are preferable and hence a good place to start there.
Hope that helps!
Adam

[#3]

Thanks Adam
My router was on channel 1. I found 2 others nearby also on channel 1 and 2 more on channel 6 so I've stuck mine on 12 now so we'll see how it goes.
Fingers crossed and thanks for your reply,
Andy