i found this on the net thought i would share it with you all
The Basics - Temperature, Humidity, pH and EC
Getting the basics right when growing your favourite plants is absolutely critical to success. Plants like us do not like extremes of temperature, humidiy, pH or EC. If you can get the basics right your plants will thrive if you get them wrong you will prevent your plants reaching their full potential and possible even kill them. Below you will find some guidelines for achieving a model growing environment.
Temperature:
An ideal temperature for your plants when your lights are on is 26°c to 28°c. A slightly higher temperature wouldn't be a disaster but too much over 30°c and you'll run into problems as the plant expends a lot of energy trying to keep itself cool and photosynthesis slows down resulting in underdeveloped flowers and fruits.
At night you don't want temperature to fall below 15°c and the closer you can keep your room temperature to your daytime temperature the better your plants will perform. If there is a big difference between these two temperatures your plants will stretch and grow quite spindly. Conversely if your night and day temperature are quite close say within 4 degrees you would see very tight flower and fruit formations and high yields.
Humidity:
Humidity is not a key factor in growing but too low a humidity will slow growth and too high a humidity will cause pathogens to flourish. Humidity of 40% to 65% would be ideal, what you'll find is that humidity will rise throughout your growing cycle as the plants take on more water as they get bigger.
pH:
PH is critical to the plants ability to uptake nutrients and additives. In soil PH should be in the range 6.0 to 7.0, in hydroponics PH should be in the range 5.8 to 6.2.
In recirculating hydroponics PH rises as the nutrient goes around the system so some schools of thought say you should start the PH lower at around 5.5 to allow for this. In a perfect world you would adjust the PH every day or so to 5.8-6.2 but if this isn't possible starting at a lower PH around 5.5 in recirculating systems would be a good idea.
EC:
EC (electrical conductivity) is a measure of the strength of your nutrients in water. To measure EC you will need either an EC meter or BlueLab EC truncheon. Some growers rely on the dosing instructions on the back of the bottles but this leads to a lot of guesswork, accurately measuring and adjusting your EC levels is the key to successful growing so get am EC measuring device they will pay for themselves, trust me!
As a good rule of thumb anything under EC1.0 is too weak and anything over EC2.0 is too strong. Good growers will start there rooted cuttings , small plants on EC1.0 and then ease the strength up over time so they get to around EC1.6 by the time they go into flower.
Different nutrient manufacturers will recomend different EC levels and it can be hard to know what to do. Keep an eye on the leaves of your plants, if just the tips show a bright yellow discoloration this is called "Tip Burn" and your feed is too high, if your leaves go completely yellow inexplicably your nutrients could be too low.
If you are going to run your nutrients at a high EC try to ease your plants into it. Start them at a weak EC of 1.4 at the start of flowering for example and then up it by 0.2 each feed, this way plants can tolerate a higher EC wheras if you start them at the higher level you would poisin them.
