Have a basic 24 site hydro cloner started of good but by day ten they had no life left to give good early veging plants. Have a 75 l/min pump that constantly runs is this pump too big for a 24 site cloner? And had trouble settling with a depth for their stems to sit in water first it was just the tips of them I decided to have submerged then it changed to having them submerged up wards of 2 ish inches. I uses general hydroponics rapid rooter with a very light dose at 1/4 ml per liter with about a 2 1/2 gallon resavoir ph between 5.8 and 6.3 back and forth. Water temps reaching upwards of 78-80 degrees in day and 68 to 75 at night. Room temps were around 75-80 F• low external temperature swings around 5 degrees between night and day temps. Tried to do my best but something went wrong developed a jelly like substance on stems as well. Never saw any sights of thriving bacteria or pathogenic water(gunk foam this sort of thing) WHAT COULD I HAVE DONE WRONG!!
I’d make sure the humidity stays above 75% and you need to keep the air moving in there.
I use above the same technique but I use hydroguard to fight the bad microbes.
Water temp air kind of high but air movement and beneficial microbes are my tack.
Post some pics Growmie 
You know I didn’t snap any and I wasn’t even gonna post I lost em but it was bugging me so I decided to post it hoping some one been through same I had got some things that looked liked roots like white bumps on the stem but never turned into roots and I was on day 15 already
The jelly like substance was on the stems inside the cloner submerged didn’t gunk up my cloner or dirty it at all
That’s sounds like Damping off is a fungal disease that affects seedlings and young plants. It is caused by a variety of fungi, including Rhizoctonia, Fusarium, and Pythium. [The disease can cause the plant to wilt and die, and it can be difficult to control once it has started]
Keep the stems and rapid rooters out of the water. Slightly above. Should solve the issue. I think you have them submerged to deep. They need oxygen as well.