Why Contact Time for Filtration Media Really Matters (& How Tank Size Plays Into It)

A Sand Media Filter in Backwash Mode

When you’re setting up a water filtration system, most people focus on the type of media they’re using, activated carbon, Greensand™, DMI-65®, whatever does the job. But here’s the thing: the contact time for filtration media (aka how long your water hangs out with that media) can make or break your system’s performance. And yep, that has everything to do with your tank size and jacket height.

What Exactly Is Contact Time?

Think of contact time like a conversation. If you cut someone off after a few seconds, you’re probably not getting the full story. Same goes for water and filtration media.

• With granular activated carbon (GAC), water needs time to sit with the media so chlorine and chemicals can actually be captured.

  
  

• With DMI-65®, it's a little different; it needs a long chlorine soak (at least 3 hours, overnight is even better) to activate its catalytic surfaces. After that, it runs on continuous chlorine feed and backwashing, not on traditional contact time, to knock out iron and manganese.

  
  

• With manganese dioxide or Greensand™, you’re looking at oxidation reactions that require a longer “chat” with the media.

If the water zips through too fast, it doesn’t matter how fancy your media is; it won’t fully do its job.

How Tank Size & Jacket Height Change the Game

Here’s where your tank size (and its jacket height) comes in. Both determine how long water stays in contact with the media.

• Tank diameter controls how fast water moves through. Bigger diameter = slower velocity.

  
  

• Tank height (or jacket height) controls the depth of the media bed. Taller tanks = more travel time for the water.

  
  

• Flow rate ties it all together. A high flow rate in a small tank? That’s a recipe for short contact time.

Basically, your tank is like the stage, and your filtration media is the performer.

If the stage is too small, the performance gets cut short.

Why Sizing Your Tank Right Actually Matters

Too many systems get set up with the wrong tank size, and it shows.

• Undersized tank → water shoots through too fast, contaminants slip by.

  
  

• Oversized tank → not always terrible, but you may end up wasting money and space.

  
  

• Properly sized tank → just-right contact time, reliable filtration, and media that lasts longer.

  
  

It’s less about “bigger is always better” and more about the appropriate system.

Water treatment isn’t just about picking the right media; it’s about giving that media enough time to work. Contact time is the MVP of filtration. And since contact time is directly tied to tank size and jacket height, getting those dimensions right is key to clean, safe, and consistent water.

So if you’re planning a system (whether it’s for your home, a well, commercial setup, or industrial project), don’t just focus on what’s inside the tank. Make sure the tank itself is sized to let the media actually do its job.