I haven`t luck with my BubbleCloner. Good temperature and humidity and only one rooted

Hello fellas. Time ago I made a BubbleCloner with an air pump, neoprene rings and an acuarium heater.
The temperature and humidity was great. Around 25ºC for the water and around 18-19ºC for the dome. I was used a plastic dome too.
I have not luck. Only one rooted. I have seen that the stem of the cuts become like gelatine or stem rot. What its my problem? I dont know. I thinked that i was doing the things good...

Possibly

air pocket got in the stem
Rooting hormone
Over/under saturation of rockwool
Lighting
Root temps too high (personal opinion) lower water temp higher disovled oxygen content. I like 19/20 C or around 68F

Roll a joint, relax and watch that video. DR Harley Smith is a very educated man and runs a channel on YouTube called NPK Industries. Lots of interesting stuff on there.

Have you tried higher temps?
Try water max ~24-25 (~75)...good there... and dome area around ~26-32 (~80-90).
You should see condensation on the dome walls...dont spray plants only the dome.
Best of luck and happy growin'

I agree with dome temps actually good shout mak'er grower.

I've never actually used a heater in my cloners tho :/ and find lights give a good enough heat in my domes.

Humidity should be 90%+