Water

For most indoor growing applications whether growing in soil or with hydroponics, tap water is the best water to feed your plants with. The excess Chlorine sometimes associated with tap water can be dissipated by standing the water in a container open to the air for a few hours before use (12 to 24 hours). Sometimes excess chlorine can make the leaves twist and contort out of shape, so we would always advise allowing your water to stand before adding to your system or watering.

Apart from the excess chlorine, tap water is excellent to use. Whether it is hard or soft water, it’s clean, bug and bacteria free and should give you no growing problems. Do not use de-ionised or distilled water and always choose tap water over rain or well water.

The pH of tap water will vary from 5.5 to 8.5. For practical purposes the lower the pH the softer the water and the higher the pH the harder the water. Added chlorine will also affect the pH, so let it dissipate before testing. Before adjusting the pH, add any necessary feed as this may also affect the pH.

Soft Water

Soft water generally has a low pH due to the low amounts of calcium bicarbonates and other ‘light’ atoms and ions in the water. You can use the pH of your tap water as a guide when choosing whether to use a Hard or Soft water hydroponic feed. If your pH is between 5.5 and 7.7 then your water is not hard enough to use hard water feeds and you should use only soft water or universal feeds.

Soft Water feeds do not generally affect the pH of the nutrient solution upon make up, so some pH adjustment may be necessary to get the nutrient solution to around pH 6. Phosphoric Acid is generally used for small pH down adjustments and Potassium Hydroxide used for small pH up adjustments. A small pipette or two may be useful as only small amounts are needed.

Universal formulation feeds like Canna Aqua and Genesis Nutrients will work well in any water, although these and other universal feeds do affect the pH of the solution upon make up. These feeds cause the pH to drop slightly, making them difficult to use in very soft water. Canna Aqua seems particularly susceptible to problems in very hard or very soft water and as a result we only recommend using it if you have mid-range water hardness.

Soft water feeds – Vita Link (SW), Canna Substra (SW), Optimum (SW), GH Flora (SW), Ionic (SW), Formulex.
Universal feeds – Europonic, Canna Aqua, Genesis Nutrients.

Hard Water

The more calcium bicarbonates and other ‘light’ atoms there are in your water, the ‘harder’ it is and generally the higher the pH. For Hydroponic Nutrient purposes, hard water feeds are only for people with very hard water with a cF 8 (500ppm total) or more and a pH of about 7.8 or above. If your tap water pH is below 7.8 then use soft water or universal feeds and adjust the pH of the final solution to around 6 using some pH down.

Hard Water feeds do affect the pH of the final solution and therefore save any pH adjustment until after the feed has been added. Because hard water has a high pH, addition of a hard water feed will automatically drop the pH of the solution and reduce the amount of pH down needed.

Hard water feeds – Canna Substra (HW), Optimum (HW), GH Flora (HW), Ionic (HW), Vita Link (HW).
Universal feeds – Europonic, Canna Aqua, Genesis Nutrients.

pH adjustment

Do not adjust pH of water or feed solutions for soil or compost.

When growing in hydroponics with lots of light we must be sure that the nutrients in the solution are readily available for absorption by the roots. This means keeping the pH of the nutrient solution between a range of about 5.5 to 6.5. In re-circulating hydroponic systems, make all new solutions between this range. The pH will generally rise over the next few days but avoid adjusting the pH every day even if it goes slightly out of range. Adding too much acid (pH down) is much worse for your plant than being slightly out of the optimum pH range.

If you are using a lot of acid to reduce your pH, but your water is not quite hard enough for hard water feeds, you may want to consider using Nitric Acid as a pH Down in vegetative growth. This affects the solution less than phosphoric acid although more is needed. Alternatively try changing feed next crop to a universal feed, which will help keep your solution pH down and buffered.

pH in slabs

Rockwool - For the first few days growing in rockwool cubesor slabs, the rockwool will drive the pH of the solution up until it settles down. Soaking slabs for 24 hours in a pH 5.5 solution (with appropriate strength feed added) to help stabilize the slab a bit before use.

Water and feeds for soil/compost mixes

De-chlorinated tap water is the best choice of water. Rain and well water can be used although we do not recommend it and de-ionised or distilled water should never be used. With the buffering capacity of soil and the larger and different pH nutrient availability range in soil environment, pH adjustment of any water or feed solutions is not necessary and only adds un-necessary elements to the water and feed.

Consequently there are no hard water and soft water soil feeds, just universal ones which will work well in all types of water.

Bio-Bizz nutrients – These are 100% biological, natural and a popular match with the All-Mix compost.

Canna Terra – This mineral based feed is a clear solution and ideal for automated irrigation systems unlike most other soil feeds which would block pumps and lines. Also gives excellent yield and quality in any soil or compost situation.