it's been a couple months since I set up my tower garden.  It's doing ok considering I started in the middle of Southwest Florida heat.  Some plants are bolting due to the extreme heat.  Others are producing small fruit.  The cucumbers are struggling and zucchini is producing early sprouting of zucchini but they dry out rather quickly.  I keep my ph between 5 - 6, add a couple large bottles of ice to the reservoir each day.  Surprisingly in this hot weather, I have lettuce growing.  The vines and leaves of the cucumbers and zucchinie are growing like crazy and I have been pruning as well. I am comfortable with the accuracy of my ph testing, but how can I find out if the nutrient level in my reservoir is correct.  I started out per instruction for a newly filled reservoir, but have had to add water and nutrient a few times since.  So how do I find out my current nutrient level?