Hi Steve,

I add 'good' untreated water back into the RO water but not for micros.
Modern fertilizers are pretty good at providing everything the plant needs
and when I do need extra micros products such as Peters STEM are more
controlled. Instead I add the untreated water to help control the mix pH.
If the mix pH gets too far away from something like 5.8 the plant has a hard
time taking up the micros. In terms of N, I feed at strengths 10 to 20
times what you are using (between 100 and 200 ppm N).

Pat

"Steve Weaver" wrote in message
ups.com...
Does anyone who uses an RO unit for their water put any amount of
untreated tap water back into the RO water for micronutrients? I've
been using an RO unit for my orchids' watering needs for the last two
years. I recently found part of a blog from a few years ago that stated
anyone who uses RO water should add some (an amount wasn't specified)
regular tap water back into it in order to supply micronutrients that
the RO unit removes during the filtration process. I usually add a
little less than 1/16th a teaspoon per gallon of the University of
Michigan formulated fertilizer every time I water my plants (and the
fertilizer container says it's formulated for RO water). Does that
sound like it's enough to fulfill the nutrient needs of the majority of
orchid genera without the need to add tap water back into the RO water,
or should I still add some tap water? I thought I was doing my plants a
favor a couple of years ago when I invested in an RO unit. However,
since what I read indicated that RO water can be tricky to use since it
takes out just about everything from the water and renders it more pure
than rain water (meaning that the plants have nothing left in the form
of nutrients to absorb from the RO water), I'm starting to wonder
whether or not I've been starving my plants.