Why Does Your Hydroponics PH Drop? 4 Causes and Fixes

Hydroponic gardening is complicated, and lots of things can go wrong. All sorts of chemicals and nutrients have to be balanced for your plants to grow well. One such problem is the pH of the growing solution: if it’s too high or too low, it can hurt your plants. 

Your hydroponics PH can drop because of rotting organic matter, nutrient concentrations, or a dirty or malfunctioning hydroponic system. A short-term solution is to add plant-friendly additives to raise the pH. You can also flush the system or install a bigger air pump.

This article will look at the four most common reasons why hydroponic systems suffer from perpetually dropping pH. Of course, different problems require different solutions, so I’ll also look at how to fix those problems to keep your hydroponic plants healthy! 

Why pH Changes in Hydroponics

pH, or “percent hydrogen,” is a measure of how much “loose” hydrogen is floating around in a liquid, unbonded to any other molecule. Each plant has a specific pH range in which it grows best. 

Also, different nutrients are absorbed better by plants at different pH levels, so it’s essential to keep track of your hydroponic system’s pH level. 

Much like a fish tank, the pH levels will affect the life of your plants. For example, if the pH is high, the additional alkaline in the water will inhibit your plant’s ability to absorb nutrients. 

If you’re noticing a drop in pH, there are a few causes, including root rot, which can happen in overcrowded tanks.

Let’s take a closer look at four of the most common causes for dropping pH levels and what you can do to fix them. 

1. Dirty Hydroponic Systems

Water is an excellent place for bacteria to live. In an indoor hydroponic system, you have a perfect environment for microbes: warm, unmoving water with plenty of nutrients and energy. 

Like a pond that grows algae because the water never changes, bacteria will grow if you don’t flush your system often. 

Dirty systems like this tend to suffer from dropping pH. 

The Solution

If the pH is very low, you can add a basic pH correcting solution like the General Hydroponics pH Control Kit from Amazon.com. The kit lets you keep your pH levels between 5.5 and 6.5. If the pH is too low, add some of the “pH Up” premium solution to the water and use the “pH Down” solution for the reverse situation. 

In the short term, this method lets you keep your plants from suffering from a sudden spike in the acidity of their water. 

However, it’s inefficient to correct your system’s pH like this constantly. What’s more, keeping your plants in dirty water is unhealthy for other reasons than just pH balance. 

If you’re having persistent trouble with falling pH levels, try flushing and cleaning your system more often. 

2. Root Rot

Many hydroponics experts recommend doing frequent checks of your plants’ root systems. If their roots are rotting too quickly, your plants might be overcrowded, or you aren’t keeping your system’s growth medium fresh. 

Just like people shed skin cells, plants shed old tissue. Plants growing in nature have insects, worms, and microbes to break down their old, dead root tissue in the soil, turning it back into nutrients that the whole ecosystem can use. 

When your plants lose root tissue, they can start to rot in the water. 

Sometimes, if you don’t change the growth medium often enough, even healthy root tissue can begin to rot. This breakdown of organic matter releases acids into the water, which lowers its pH. 

The Solution

If you are flushing and cleaning your system regularly but still struggle to keep the pH from getting too acidic, try doing regular root examinations

Squishy black or brown roots, plus a foul smell, will warn you about root rot. If the affected area is small, you can try gently trimming them off. Rinsing in cool water will also help. 

To prevent root rot, you should first consider buying a bigger air pump. Sending bubbles through the water will dissolve oxygen in it, which is good for plants and helps them consume more nutrients, so there aren’t enough left over for bacteria. 

Also, it’s a good idea to check your system’s heaters. When water is warmer than a comfortable room temperature, or about 77° F (25° C), it tends to cause an overgrowth of microbes. 

3. Poorly Mixed Nutrient Solution

The nutrients added to your hydroponic system are slightly acidic. Therefore, overfeeding your plants can cause the pH to drop and plants to release even more nutrients. 

If you’re typically following the manufacturer’s guidelines and are still finding issues with your pH levels, you may need to make a few adjustments.

The Solution

If you’ve flushed out your system but it’s still suffering from falling pH levels, you are probably feeding an over-concentrated nutrient solution. 

To fix this, start by getting your base readings. You’ll need to leave the water out overnight to allow it to come to room temperature and to give you the most accurate readings. 

Using the chart provided on the package, check the suggested CF (conductivity factor) level and adjust accordingly.

For example, if the CF levels are rising, your plants will be absorbing more water than usual. In this case, you’ll need to top up the tank with plain water to prevent nutrient burn

4. Reverse Osmosis Water

RO or Reverse Osmosis water is water that has been filtered through a membrane to remove all solutes, bacteria, and minerals. It can be healthy to drink, especially for people, but plants are used to growing in water that has all kinds of things in it. 

Plus, most nutrient additives for hydroponics are meant to work with tap water from a municipal water plant, which already has some chemicals. 

The problem with RO water is its purity prevents it from holding a stable pH. Usually, even if you can add acids or bases to the water, chemicals dissolved in the water will trap or release “free” hydrogen as it is added or removed. 

This ability of water to resist changes in pH is called its “buffering capacity.” If the water’s buffering capacity is optimal, it will absorb chemicals like a sponge without any noticeable change in pH. 

The Solution

If you’re using RO water for hydroponics, you’ll need to purchase buffering compounds like CaliMagic from General Hydroponics that you can add to the water. When these products are dissolved in RO water, they give it the ability to buffer against changes in pH. 

One person who experimented with this product found it worked best when added before other nutrients and allowed the RO water’s pH to stay steady for fourteen days afterward. 


No matter what kind of hydroponic system you use, keeping your plants in a healthy growing environment is vital. For example, if the pH of your growth medium is too acidic, plants can’t absorb macronutrients properly, and the acids may hurt their roots. 

Dropping pH can be caused by many factors, but some simple troubleshooting and a few different products will help you manage pH for a robust harvest. 

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Anat Goldberg

Hi! My name is Anat and I have lived all my life in the countryside. I grew on a farm in Northern Italy and from an early age, I took care of the animals on the farm and the family garden. Over the years I have developed a growing passion for organic cultivation and pest control.

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