Well for starters, I discovered that it is easy to crush the stems if not careful when cutting. Also when I take mine I usually cut them about 4-6inches long and with several leaf nodes on them. I usually will cut just above a set of leaves so that the stem left behind doesn't embolize and block tertiary growth.
Then I cut off the section of internode(open piece of stem between leaves) so that it is about 1/4inch below the next set of leaves. I also cut those leaves off right against the stem so that some of the white innerhurd is exposed. more often than not, that is where tour first roots will spring from. I also either scrape a little of the outer skin off of the little bit of stem sticking down or split it with the blade to expose a bit of the inner hurd.
Then I dunk them right into my cloning gel and place them into the cloner puck that holds them so that about 1-2 inches of the stem is sticking down beneath the puck. I have tried leaving the rest of the leaves intact, cutting off all but the top 2-3 sets of leaves, and cutting in half all but the top 2 leaves. I have not seen any better results with one over the other.
I don't use any heat on my cloner but it sets in the room where the AC is and is kept in the mid 70s. I put my dome on them to keep the AC from blowing on them directly. I have had several clones show rot on the stem below the node and a few have actually had that little section of stem rot entirely away as the roots were growing out of the node, and they grew and thrived. I also use a "thrive alive" B vitamin nute mixed into my foliar spray and spray them once a day until they are ready to be transplanted.
About your tap water. If you haven't checked and leveled the PH you should. Also check the TDS of the tap water. If it is softened by the city, you may have chlorine, and some places soften with salt which can cause problems. I would use distilled water and clonex solution, then PH it to 5.5.