A client of mine has contacted me to say his site has gone from position 4 on google to 40, losing him over 130 visitors a day.

He investigated before contacting me and said he believes it is down to a DNS issue or change.

This could be a massive coincidence but a couple of weeks a go he was having email issues so i was checking the dns/mx information on his domain, i noticed he had 2 NS entries for old nameservers (in addition to current nameservers) so i removed them...

Is it possible these actions have caused his website to drop? i find it hard to believe, the domain, ip everything is changed, all i done was removed the 2 old name server entries.. the nameservers in question don't even exist anymore, i'm not sure why they were still in there but they were so i removed them.

I've re-added them as a precaution but i can't see it fixing the issues..

or is it that google has been at their tricks again and changed their algorithm? Is there any way i can pin point whats caused it?