my white widow auto stem looks too tall, can i add more medium to solo cup to help support stem, 5 day old plant.light is 12 inches from plant , running at 30 percent, soil is moist, light ac infinity fan running 1st setting, no exhaust running
Post a pic Growmie and let’s have a look 
welcome to the community
Welcome to the forum.
Couple of suggestions:
Young plants need very little water and cannabis prefers wet/dry cycles. Water, let the soil dry out, then water again. A 5-day old plant only needs a few ml of water per day and overwatering is by far the most common cause for loss of seedlings.
This is a symptom of too little light and the plant is most likely stretching for more light. What are you using to light the plant (brand and model)? If the light is at 30%, then turn up the light.
If you are at the point where you are thinking of adding more soil, then it is probably time for a transplant to a larger pot.
As @OGIncognito said, we can get you more precise suggestions if we can see a pic of the plant.
mars hydro ts1000
The seedling looks fine and isn’t stretching all that much. Turn the light up a bit. Be careful to not overwater her.
Those 2-prong meters are notoriously inaccurate and worthless. Apera and Bluelab both make decent pH and PPM meters.
ty will check those out, this my first grow, stem just looked thin to me
Stem thickness is fine, she’s just stretching a bit for more light.
Thanks, I added little more medium just incase