If its still getting darker then I would assume the concentration isn't an issue. Also I have two boys and we dtd every day from CD12-16 and I Od on CD14 this time we timed for a girl using OPKs worked out I Od on CD15 usually so stopped dtd on CD13 then realised I didn't O until CD19!!! I'm surprised i even managed to catch that egg so now can't wait to find out if it worked to get a little lady best of luck to you