Seels:I'm officially a sperm killer arn't i
Pretty sure that we all have done it at one time or another! Actually for DH if his pH goes below 7.5 then there is no movement at all! His sperm are super sensitive!
If you need to do a lime douche to get rid of CM and your pH is that low then just do a douche with a pH of 4 this way it will not drop your pH any lower than that.
There is always hope do not give up!! Some of those little guys can make it through the toughest conditions! 
Good luck.