Coco is pretty forgiving and there is a very wide range of acceptable levels of nutrient and pH where the plants will grow. The idea though is to keep those levels optimal for the particular crop 24/7. Depending on the crop or strain, you might find as much as a 1000ppm difference between what that level is. For the most part, I keep my input level constant and adjust watering frequency on an as needed basis. You do need to be careful not to let the coir get too dry though. Because of it's properties, it's very difficult to overwater coir as long as you have good drainage and the plants are not sitting in standing water. I monitor the runoff to tell how things are going in the root zone. If the runoff levels are high, using a longer irrigation cycle or pouring more feed/water and allowing more runoff(30-40%) will usually bring it back to where I want it. If levels are low reducing the amount of runoff will raise them. In a commercial sized operation, it's much simpler to adjust watering cycles than to constantly be changing the feed ratio of the injectors. In a smaller hand watered operation, you can much more easily increase or decrease the strength of the nutrient solution being applied which may be more economical. I still recommend checking the runoff after each watering and taking notes so you can adjust accordingly for the next watering/feeding. It also lets you know ahead of time(before the plant shows signs of a problem) if something needs to be changed. It is also not uncommon to see different levels from plant to plant in the same room getting the same amounts of water and feed which is why good note taking really is important! During periods of rapid vegetative growth, I have seen runoff levels drop considerably even with normal input feed levels and raising the feed ppm until it stabilizes keeps the plants from showing any deficiencies. If you see that the runoff ppm's are too high(usually caused by letting go too long between irrigation cycles) you can use straight water to quickly bring the levels back down to acceptable ranges without harming anything. The larger the plant and the smaller the container, the more difficult it will be to keep everything in balance and the more frequently you will need to be watering/feeding and checking the runoff. I have seen full sized plants wilt terribly when drip emitters clogged and the pots completely dried out. Pouring gallons of water over the coir, the first runoff came out over 4000ppm but rapidly decreased back to where it should be which is one of the great things about using coir. It is easy to re-wet after being too dry and easy to flush excess nutrients and bring back into balance. The effected plants had a few burned leaves at the top but quickly recovered and produced normally.
Factors that will effect frequency and strength of the feeding/watering cycles are quite numerous so there really isn't a set formula to give and every grow will require fine tuning. Daytime temps, night time temps, RH, light intensity, pot size, plant size, plant age, and even strain will all come into play.
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