Removing Substrate from an Established Tank

I’ve replied to this in Facebook groups a few times, so I decided to write this up to make it easier to share. Unfortunately, I am not planning on doing this soon, so there won’t be any videos or photos. But yes, I have done this before to remove a sand bank from my 600 litre (180 US gal ) planted tank.

This will only work for substrates that are fine and light enough to be siphoned with a hose.

You will need:

  • At least 2 large pails (or any convenient container),
  • A large 200 micron or finer filter sock, and
  • A hose.

This will take some time, so put aside a few hours or an entire day to do this, depending on the amount of substrate you need to remove.

The first step is easy. Just start a siphon into a pail and start to siphon the substrate. Do not use a substrate vacuum attachment. Those are designed to leave the substrate in the tank while the lighter detritus are lifted out. In this case, you want to siphon out both the substrate and detritus. This should leave the water in the tank clean. Be gentle moving that hose around to avoid stirring up the detritus before your siphon gets them. You will also need to adjust how fast/much you siphon up the substrate to avoid choking the hose.

The problem with siphoning out substrate is that you often do not have enough water in the tank to siphon out all the substrate. And you also don’t want to replace all the tank water with new water. So this next step is to make sure we don’t run out of tank water while siphoning the substrate out. When your pail is full, stop the siphon. Let the pail sit and wait for the detritus in the pail to settle. Once they have settled, siphon or scoop the water in the first pail through the filter sock and into the second pail. This should filter out the finest detritus and leave you with pretty clean water in the second pail. Transfer that water back into the tank. Dispose the substrate in the first pail. Repeat from the first step.

If you plan to add new substrate, watch my video on how to add substrate to an existing tank.

Once you are done, do a regular water change to get rid of any detritus that got stirred up. And sediments if you added new substrate.

Some Tips

  • If you have more pails, then you can continue to siphon while the detritus in the previous pail(s) settle. This will save some time.
  • If you have a sieve and time to spare or helpers, sieve out the substrate in the pails (before letting the detritus settle) so that you can recover more tank water.
  • You shouldn’t have to shut down your filter as long as you keep the water level in the tank high enough and you avoid stirring up too much detritus.
  • Do a filter maintenance a few days later as it would have picked up some of the detritus and sediments.
  • If your substrate is planted, you can leave medium/large plants planted, but hold the base of the plants as you siphon the substrate from around and under their roots.
  • For fine carpet plants… I haven’t really thought this through. I can think of a few ways:
    1. Pull up the plants as you siphon. This should work for carpets plants with lots of runners.
    2. Vacuum the substrate first, then gently remove the plants completely before siphoning out the substrate.
    3. Turn off the filter, gently remove the plants, wait for the detritus to settle, then start the siphoning as mentioned.
    4. Siphon the substrate from under them and let them float up as the substrate is removed.

I hope that helps. If you have questions, use the comments below.

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