Hydroponics, Plant Nutrients 

Correct pH control is a critical but often overlooked aspect when growing in hydroponics or soilless mediums like Coconut Coir or Sunshine mix. In its simplest context, the pH of your solution determines how much of the mineral elements you supply your plant is accessible and ready for uptake by the plant.

The term pH, refers to a scale from 1 t o 14 that measures the acidity or alkalinity ( concentration of hydrogen or hydroxyl ions )  of a solution.  1 is extremely acid and 14 is extremely alkaline with 7 being neutral ( equal concentration of hydrogen and hydroxyl ions ). This scale is what’s known as a logarithmic scale meaning that for every one point increase or decrease in pH reflects a 10 fold change in acidity or alkalinity. For example a pH 6 is 10 times more acidic than a pH 7 and a pH of 5 is whopping 1,000 more acidic than ph 7!
You can see then how quickly things can change or get out of control in a hydroponic solution.
Plant nutrients are available across a range of pH with the optimal pH being 5.5 for Hydroponics and Coco Coir and a slightly higher pH of 6.3 for soil based systems. These 2 pH values represent the values that allow the plant to take up the maximal amount of all mineral elements. Go too far above or below and certain elements begin to become unavailable to the plant.
Get this simple control wrong and your plants will suffer suboptimal nutrition at best and at worst your plants will suffer from multiple nutritional deficiencies or even die in extreme cases. 

The best way to control pH is via the use of a common acid ( pH down ) and alkali  ( pH up ). The best ones to use, and ones which are available at all good hydroponic or gardening stores is Phosphoric Acid for pH down and Potassium Hydroxide for pH up. These are chosen because they do not add harmful elements to your nutrient solution. Phosphoric acid adds Phosphorus and Potassium Hydroxide adds Potassium both essential plant nutrients.

Once people realise how important pH is to their crops success, their natural tendency is to over manage the pH of the solution. In our desire to keep the pH at the most optimal value many gardeners adjust their pH when it moves even the smallest amount from the ideal value. However, in doing so many gardeners actually sabotage their own results - in the most unlikely way.  When gardeners over control their pH they inadvertently add large amounts of either phosphorus or potassium. This can cause the nutrient solution to become unbalanced and elements to begin to be locked out as the nutrients interact with each other in undesirable ways as the concentrations of particular elements become too high. This is most often seen with the use of too much pH down which can cause Phosphorus induced zinc deficiency. The common symptom of this deficiency is small or underdeveloped flower s - not what we want to experience!
The best way to control pH is to start with a well balanced nutrient like Dutch Master GOLD NUTRIENT that doesn’t shift pH excessively. GOLD NUTRIENT’s unique technology allows it, in most situations, to remain within an ideal pH band.  Once you have set your initial pH to either 5.5 ( Hydro or Coco users ) or 6.3 for soil users then there is no need to adjust it until it either falls below 5 or above 6.2. pH will naturally fluctuate from day to day as the plants draw on different ratios of elements. In most cases, with a good nutrient like GOLD NUTRIENT, the pH will stay within this range and will not need to be adjusted often. Generally the pH of a solution tends to rise during the grow cycle ( as the plants take up more nitrogen which causes the pH to rise ) and to fall during flowering when the plant has a preferential draw on Phosphorus.
As the mineral elements in a nutrient solution are quickly used by the plant, it is a good idea to replace your nutrient solution at least once every 2 weeks ( in hydro ) or to flush at least 2 times a week ( in soil ). The other important time to replace your nutrient solution is if it raises or lowers by a full point or more within 24 to 48 hours. This either indicates the plant is under stress, or more commonly the plant is rapidly depleting the nutrient solution of either nitrogen ( when the pH goes up ) or Phosphorus ( when the pH goes down ).

pH can be measured using colormetric strips ( that run a particular color when dipped into the nutrient solution ), pH indicator solution ( this also turns a particular color at different pH values and is matched to a color chart )  or a pH meter. The first 2 options are very inexpensive and are great for those on a tight budget but the best and most accurate way is to use a well ( and often ) calibrated pH meter. A good digital pH meter can be bought for under a hundred bucks these days and is a great investment, along with a good calibration solution to keep it accurate.
As we can see pH is very, very important but controlling it is a simple and relatively stress free procedure.

Prior to calibrating your meter it’s a good idea to place a small piece of foam, soaked in pH buffer 4.0, into the end of your pH meter probe cap. This will ensure that your probe remains suitably hydrated and will maintain its full life.
Calibration and care of your pH meter is vital if you are to get accurate readings. An incorrectly calibrated or poorly maintained pH meter can cause as many, if not more problems as using no meter at all! Calibrating and maintaining your pH meter is simple and takes virtually no time at all! For greatest accuracy calibrate your meter at least weekly using good quality calibration solutions and a 2 point calibration check. Calibration solutions for pH meters are called buffer Solutions. It is vitally important to use both pH buffer 4.0 and pH buffer 7.0 to ensure that you have the greatest meter accuracy and to ensure that your pH probe is not worn out.

To calibrate, first begin by decanting a small amount of pH buffer 7.0  into a small receptacle just big enough to immerse your pH meter probe into. Never dip your meter directly in the bottle of buffer solution or return any used buffer to the bottle. This avoids contamination and inaccurate readings. Now dip the probe of your pH meter into your small receptacle and calibrate to pH 7.0 according to your meters calibration directions. Next, rinse off your probe and receptacle in some clean water, shake the excess water and fill your small receptacle with pH buffer 4.0. Now dip the probe of your pH meter into the receptacle. Your meter should read within 0.2 pH points of 4.0 ( pH 3.8 to  pH 4.2 ). If your meter does this then congrats – you just calibrated your pH meter! If your meter reads either above or below the figures listed then we need to re perform the calibration sequence but in Reverse. To do this once again insert your probe into the pH 4.0 Buffer solution and perform your meters calibration sequence. We have now just calibrated the meter to pH 4.0. Now rinse your pH probe and the receptacle in some clean water and shake the excess off. Next, decant some pH buffer 7.0 into the receptacle and dip your pH probe into the receptacle and once again calibrate the meter ( this time to pH 7.0 ). Now rinse the probe and the receptacle again and recheck at pH 4.0. This time your meter should read within 0.2 pH points of 4. If it does not, then it means your pH probe has come to the end of its life and needs to be replaced. In most instances this means you will have to replace your meter if the probe is not detachable.