Weird build up on bottom of clones

I have some clones around 15 about 10 days old in a homemade bubble cloner. I left them for the 10 days and came back and the ph was a little high, and non rooted which suprised me as before a good amount would root in 7 days and the other by 10-14 days.

I changed the water and adjusted it to 6.0. A couple of days later there is this cloudy substance around the bottom of the stem on some of them, I'm not sure maybe it's stem rotting? Any help is appreciated....

I tried to take pictures but my camera sucks.

thanks
-Juke