Longtime lurker, first-time poster, I'm utterly desperate for advice at this stage. I've spent the last few months setting up a hydroponics system for tomatoes/cucumbers, and *I thought* it was good to go. I've been using a ChemPak Hydroponic powder mix to make the nutrient solution, and using citric acid as necessary to adjust the pH. I'd taken advice from Daniel Fernandez on this, although I've been using tap water rather than distilled. I've kept solutions in bottles in the kitchen for many weeks, and their pH's have remained very stable.

Imagine my horror then last Sunday when I finally set up the entire system with solution - and added the aeration stone - when within hours the pH climbed from an initial 5.88 to 6.69. Huh?! I added more citric acid to bring the pH back down to 5.6. Again, within hours it had climbed back to 6.8. Left for 24 hours plus, it ends up at around 7.13 - and changing to a different reservoir makes absolutely no difference to this effect.

I then ran an overnight experiment. I made up fresh solution and divided it into four bottles. One bottle stayed in the kitchen, the three others went into the greenhouse - one also closed, one open and a third with an airstone bubbling in it. Next morning, the only bottle to show a pH change was the aerated one - up by several tenths of a unit. I've repeated the above experiment using both tap water, and Brita filtered water too (sadly). Aeration increase my pH by a lot - and citric acid doesn't help for very long.

My water is hard - around 100mg/l total hardness I think, and is probably the main issue, it has a pH out the tap of around 7.9. I came across greystoke's post below (sorry, don't know how to quote properly), and wondered whether anyone else has had success with his technique, i.e. pre-bubbling, then adjusting with vinegar, before adding any nutrients?

Really, any advice would be greatly appreciated!

**************************

* Posted by greystoke Mediterranean (My Page) on

Fri, Mar 14, 08 at 2:39

This may be useful although perhaps a little off-topic.

Here in Africa  rain is at a premium, and many things are not readily available, so . . . we DIY a lot.

If tapwater is too hard and/or the pH too high we manage to deal with that with simple means.

Hardness is a result of the calcium and magnesium content of the water. It can be measured using a hardness tester bought at an aquarium shop. The test provides two measures:

GH (for General Hardness) is a measure for the total of calcium and magnesium content given in mg calcium oxide (CaO) per 100mL of water.

KH (for Karbonate Hardness) is a measure for the calcium and magnesium bicarbonate content. Also given in mg calcium oxide (CaO) per 100mL of water.

Naturally, the KH is part of the GH, and is always smaller, unless thereÂs a foreign bicarbonate in solution.

Bicarbonates are strong pH buffers which resist lowering of the pH.

The best way is to store the water under an aerator for a few days, and bring the pH down using a measured quantity of 5% white spirit vinegar. This will turn the bicarbonate ions into water and CO2 gas which will be driven off by the aerator. WhatÂs left is calcium and magnesium acetate.

Quantity: 0.4mL vinegar per Litre of water, per degree KH hardness.

*****************************