So you set the pH of your hydroponic reservoir to 5.5 only to return 2 days later to find the level has risen to a pH of 6.0! You’re wondering why the pH won’t stay where you set it?
The nutrients you add to your reservoir are acidic. When the plant consumes these acidic nutrients, the natural reaction is a rise in pH. This means it is normal for your reservoir to have a natural pH up-swing. It is much more desirable than your pH dropping, which would indicate you have too much nutrient in your solution. Here is a cheat sheet:
pH goes up, EC goes down = Plants are feeding. Potentially raise nutrient levels.
pH goes down, EC goes up = Plants are putting nutrient into the water rather than taking them out. Nutrient levels are too high.
pH stays stable, EC levels stay stable = Equilibrium. Plants are taking equal parts nutrients and water. Maximum growth is occurring.
It is best to error on the side of caution and slightly underfeed you plants . This will encourage the natural pH swing from 5.5-6.2. Once your solution reaches the 6.2 mark it should be brought back down to 5.5 pH and allowed to slowly drift up again. The reason this is ideal is that the plants are able to take up specific nutrients more efficiently at different pH levels. By going up and down through the proper pH range the plant has good access to all nutrients required for optimal growth.
Having the ability to monitor and adjust nutrient and pH levels in this fashion are one of the main benefits to an active or recirculating hydroponic system.