These are my steps for a brand-new water change. This can be done in the DWC water reservoir or a separate container and then transferred to your water reservoir. I recommend having a second container the same size as your primary DWC container. This way you can swap containers, allowing you to clean one while the other is holding the plants and roots.

Use cold tap water only. Hot water tanks are rarely cleaned and often have pathogens sitting in the water tank. You do not want this in your DWC system. If using distilled water add Cal-Mag (I wouldn’t bother with distilled water unless you tap water is very hard or you are on well water). If your groundwater is cold use a fish tank heater or immersion circulator to bring up to a minimum of 62F. Water below 60F will stunt the plants growth. Add nutrients. Use this nutrient calculator to determine the nutrient quantity. For Veg only: Add Silica to improve cell wall strength. Adjust pH to 5.50 Record starting pH and EC in grow journal

Immersion circulator being used to heat cold tap water

Top-Up Vs Full Water Change

Always do a full water change if there is excessive organic matter (root fragments) floating around

If the water/reservoir smells musty do a full change

If your temps hover around the high end of the acceptable range (69-72F) you should do more frequent water changes

If you have any signs of root-rot, do a full water change

Do a full water change within 2 weeks of flipping to 12/12

If possible sanitize the water reservoir with star-san when doing a full change.

The auto-siphon is a cheap and sanitary way to transfer nutrient solution

How Often do you need to Clean DWC Water Reservoir?

I typically only clean my DWC water reservoir after harvest (before starting the next batch). Of course if you are having issues with root rot I would recommend cleaning and sanitizing your water reservoir every time you do a full water change. If I am not having issues I will rinse the container after doing a full. water change but won’t bother with sanitization.

Star-san is my preferred sanitizer for DWC water reservoirs. It is the number one sanitizer used by homebrewers and is readily available online. I will usually use dish soap or oxy clean to remove and salt and biofilm before sanitizing.

Star-san is an acid-based sanitizer that is non-rinse and food safe. This means that after swishing it around your reservoir and dumping the remaining foam it does not need to be rinsed out. It will be neutralized immediately after adding water. As brewers say, “Don’t fear the foam!”