If you want to increase the growth of your indoor-dwelling plants, but have little space or time to do so, you should consider hydroponic gardening. This method of gardening involves growing plants in a water-based, nutrient-dense solution without the use of soil. 

If you’re reading this article, you likely already know that, and you’re probably already aware of the many benefits of this modern style of gardening. But are you aware of all of the intricate details surrounding this process?

There are several types of hydroponic systems, but one thing they all have in common is that they house a nutrient solution within a reservoir. This reservoir must be changed every one to three weeks, and a failure to do so can spell disaster for your plants. However, this time estimate varies depending on what plants you are growing as well as your specific set-up, so knowing the reasoning behind why and how to change or empty your reservoir and nutrient solution is even more important.

Knowing when to empty your reservoir and nutrient solution can be tricky. Here’s how to do it.

Unlike plants grown traditionally in the soil, a hydroponic plant only has access to the nutrients in the water. If you fail to keep your reservoir water clean and balanced, your plants will have a reduced ability to uptake nutrients and an increase likelihood of problems related to nutritional deficiencies.

In a hydroponic garden, your water levels will decrease naturally for two reasons. One, the water from the tank will evaporate into the air over time, and, two, of course, your plants will absorb some of it – as you want them to! However, once your water levels reach a critical point, the roots will stop receiving the required nutrient solution.

This is problematic in two conflicting ways. In the first and most obvious, your plants’ growth will be stunted and altered as a result of a lack of nutrients and appropriate watering. In addition, your nutrient solution will become more and more concentration in the diminishing amount of water, meaning your soil can eventually burn the roots with too manynutrients.

Keep an eye on your plants for signs of nutrient deficiency, which can indicate that it’s time for your water to be swapped out. Nitrogen deficiency is indicated by a yellowing of leaves and stunted growth, while too little phosphorous can cause your plants to turn a blue, purple, or red color. If your plants are lacking in other nutrients, you might notice drooping or discoloration as well. 

When you’re ready to replace or top off your reservoir, start by blending nutrients and additives and combine them with prepared water. Make sure you test your nutrient solution repeatedly before you add it to the tank.You should keep an eye on your plants for the first few days after replacing or topping off your reservoir, as your water levels will drop significantly in this time as the plants rapidly absorb water. 

It should be noted that water will be absorbed more quickly than nutrients will, which is what leads to potential over-concentration of the solution. To prevent this, keep a note of the high-water mark in your tank, and check the water level daily. If it drops below the mark, top it off with plain water. This should be done every few days until you’re ready to replenish the entire solution. 

Monitor your pH carefully with your meter. Ideally, you want your solution to hover at around 6.5, but this may vary depending on the type of plant you are growing. Keep an eye on the pH and electrical conductivity in the reservoir, and add nutrients whenever necessary after you’ve topped of the water. 

It’s not enough to use pH as the only method of determining when to add nutrients.  You also need to pay attention to the electrical conductivity (EC) in the reservoir, since this will tell you how much salt has dissolved in the water. Monitor both for best results. Once the amount of water you’ve added via your regular topping off has surpassed half of the reservoir capacity, you need to change the solution out altogether. 

Because plants take in nutrients and water at different rates, there is really no hard-and-fast rule on how often you should empty your reservoir and nutrient solution. Waiting too long can cause a build-up of certain minerals, while changing too often is cumbersome and can disturb your plants. Nevertheless, this is an important step, as water changes allow you to start fresh with a clean, chemically balanced reservoir.

It is incredibly important to monitor your hydroponic garden to be on top of any changes or problems that may arise. Daily checks are best, but checking twice or three times a day is a good rule of thumb to follow if you have just changed or added something in your system. No nutrient solution is perfect, so if you notice clogging debris, chemical imbalances, or bacterial infections, you may need to adjust your solution.

In some cases, this may necessitate flushing the solution altogether. It’s actually recommended that you do this at least once a month to cleanse the system even if you don’t have any obvious problems.This can help remove any built-up residue that can affect the growth of your plants. 

Keep in mind that you will need to clean your reservoir from time to time, too. While you should always keep a tight lid on the tank to prevent algal growth and to reduce the likelihood of foreign objects -  like dust, dirt, or, yes, your cat’s curious paw! - from reaching the solution, this doesn’t keep everything out.

Every time you flush your tank, wipe it down with a safe cleaning solution like hydrogen peroxide. This is also an excellent opportunity for you to clean or change filters, rinse dirty strainer bags, and to tidy up the tank. 

Over time, you will learn a system that works best for you, and for the plants you are growing. Keep accurate records of how much water and nutrient solution you have added each time, and record how well your plants respond to different combinations. 

 While each plant and each hydroponic system is different, a bit of vigilance when you’re first getting started can help to make the difference between a so-so crop and one that is truly spectacular.