If you read this site (that is a facade for a RU seller) you will see the problem is with any solution that contains water.
http://www.ru58841.info/stability-and-storage/
Rogaine only comes with both ethanol and water. I think you need a minoxidil solution that has no water at all.
They say:
There do not appear to be any published studies on the stability of this compound. However, nilutamide, a compound with a similar chemical structure, has been evaluated (2).
Nilutamide is stable in acidic solutions and is fairly heat-stable. However, it breaks down rapidly when exposed to light, and when dissolved in a solution containing water, it is <strong>subjected to hydrolysis and breaks down fairly quickly</strong>. Extrapolating these results to RU58841, if the compound is dissolved in pure ethanol (and keeped in the dark) it is probably stable at room temperature, as reported by Anageninc. However, applying a solution of RU58841 dissolved in pure ethanol to the scalp will cause significant irritation and damage to the skin, hair, and hair follicles. It is also possible that very little of the RU58841 will be absorbed unless it is dissolved in a solution containing water and some type of polar compound or polar carrier, such as the emulsifiers in K&B Solution.
PS: does your stemoxydine lotion (serioxyl?) contain any water?