Reverse osmosis will drop the Chlorine, heavy metal and mineral content of your tap water to almost nothing
Sodium, Calcium, Magnesium, iron, copper , manganese, cobalt, boron , molybdomen, sulfur will also be removed.
This is good if the tap water is high in Chlorine, Sodium, and undesirable salts , and bad because these chemicals are needed
If using RO with hydroponics, with inert media such as rockwool, some minerals need to be added to the water to achieve the proper balance.
Often hydroponic nutrient blends, assume you will be using average tap water, and these blends are not boosted to the mineral level needed with RO water . So after analysing the nutrient formula you use, you may wish to add Cal/ Mag or some source of minerals.
For example: tap water at 500 ppm Total disolved solids(TDS) , can be reduced to 15 to 20 ppm with R.O..
A mineral suppliment that raises the TDS up to 100- 200 ppm,, with the desirable minerals, would be a benefit.
A nutrient formulation may suggest 1200 ppm is a good concentration for their formula.
With tap water at 600 ppm in disolved solids , that would mean only 600 ppm of the nutrient formula is necessary.
If you are using RO water at 20 ppm , then to obtain a TDS meter reading of 1200 ppm , you would need to add 1180 ppm of the nutrient formula. That is 2x as much nutrient fertilizer as the average tap water user is putting on the plants.
In the vegetative phase , you possibly could show a mixture of mineral deficiencies. Even though the nutrient(N P K) levels were sufficient , without enough minerals, the nutrient fertilizer is not metabolised efficiently. You could easily be overfertilizing and still show deficiencies of some nutrients , and nutrient burns caused by other nutrients building up.
Most people would try :
1. flushing - you remove more minerals, possibly compounding the problem,
2. Add more nutrient fertilizer - you fertilize more , you get nutrient burn.
3. Foliar feeding - If you think you have a leaf burn now, try a little foliar, it will cook em good.
Save this for later when the plant has cleaned out its salts.
If you have been using a Heavy Nutrient Feeding schedule, then as the plants go deeper into bloom
The nutrient uptake will be slower , and everything can worsen.
Flushing, using any of the standard methods, should be considered , It may stress the plant out for a day or two, but removing the high concentration of fertilizer is the initial step.
Follow the flushing with a balanced mineral and nutrient concentration between 700 ppm and 800 ppm .
Stay with 800 ppm feedings until the end. These plants have been damaged, many are not capable of using high-fert concentrations. If you push them , they won't respond very well .
The next crop will be much better
Even if you have supplied a good balanced mineral suppliment, If you Go by a TDS of 1200 ppm , there will continue to be over fertilization burns, and deficiency symptoms
Because with reverse-osmosis, you are not carrying the extra Salt load (300 ppm to 500 ppm)
So subtract that salt from the 1200 ppm
With reverse osmosis use a mineral suppliment , most all nutrient companies now have such a thing, and then only bring the nutriemt conentration up tp 800 ppm or so, while in bloom.
You can go higher during vegetative.
Raise the levels slowly , if you see the need, but do not jump from 800 ppm to 1200 ppm in one day, plants take time to manage such large changes
Common Symptoms are a mix of deficiency and over feeding , yellowing of oldest leaves,, purple petioles and stems, brown spotting between the veins of many leaves.
Servere deficiency of some minerals affect the growing tops , they will darken and die, which destroys the plant.
Moderatete to severe problem, the plants will not grow, or grows slowly , reducing the yield of flowers tops.
Adding Epsom Salts Mg2 - SO4 will help, but is not the entire answer. there may still be a problem of mineral inbalance, that willl appear sooner than later;.
For these complex deficiencies a visual analysis of the stem and leaves, is not reliable enough.
There is too much overlap of symptoms , to say that it is undoubtably this or that imbalance.
You can see the lack of magnesium, and Iron, Calcium not as apparent. THe browning iof the leaves is a chemical burn ,
The yellowing of older leaves is so common to many plant nutrition problems
A diagnosis can be made , with soil analysis and plant material analysis for minerals and nutrients, Very few growers will feel the urge to send some weed in for analysis.
If using R.O. add a mineral suppliment, and reduce the concentration of the nutrient formula used , especially during bloom.
The R.O. water is pure and without all the undesirable salts , found in most tap water ,
RO plants have a smoother smoke,
They grow extremely well , but it takes some extra reading, daily monitoring, and a better understanding of the plants needs.
Actually you need to be familiar with the minerals, so when you purchase , minerals, you will have confidence in your decision.
The best pictures and description of these nutrient problems, that I have seen are right here on Roll it up
Yes, you will want to set the proper pH of the Watering solution, at all times, whether Flushing, feeding , rooting, sprouting .
If using a soil mix , instead of inert hydroponic media, there is a built in buffering system, and compensation, that will mask the water's mineral deficiency for a considerable length of time.
