Filter Floss – It Can Have a Big Impact on Your Aquarium

Filter floss creates quite of bit of controversy in the aquarium hobby.

Many experienced hobbyists consider it an key part of successful reef keeping. Others argue it does more harm than good.

Those who swear by it say it’s an easy, effective tool that helps to keep your water clean and your nutrients under control.

And those who do not believe in it say it is unnecessary. And, if not changed regularly, will act as a ‘nitrate factory’ that can harm your tank. They say all you really need is a skimmer and regular water changes and your tank will do fine.

I did a lot of research on forums like and before I set up my 24g aquarium.

And at the time I chose to not use filter floss or a filter sock. Instead I chose to simply rely on small weekly water changes to keep my water clean.

And I have to admit, it seemed to work. My phosphates and nitrates were always a bit high:h PO4 hovered around 0.25 ppm and nitrate around 20 ppm.

I didn’t have any algae problems and my fish and corals seem happy.  At least, until I added SPS coral.

The SPS corals did not like the high nutrients.

So, I added a skimmer.

After running the skimmer for 2 months my nutrient levels were climbing nearly as much between water changes. But they were not dropping significantly either.

Then I decided to give filter floss a try.

Within 4 weeks my nutrients have dropped by more than half.

My phosphates are already down to 0.12 ppm. And, even more surprising, my nitrates are down to 8 ppm.

The optimal levels for a tank with SPS coral in it are less than 0.03 ppm of phosphate and 2-5 ppm of nitrates.

At this rate I should reach them in no time.

So, it looks like both sides of the argument are right..

Filter floss can be a very good, very simple tool in the battle to keep your water clean IF you change it regularly.

Have a look for yourself…

This is what the filter floss looks like new.  I cut into 1″ strips so I can stuff a piece in between the baffles in my sump.

filter floss cut into strips
Filter floss cut into 1 inch strips.

And this is what it looks like when I pull it out one week later during my weekly water change:

dirty filter floss vs clean
Filter floss after 1 weeks of use (bottom) versus new (top).

If I were to leave the same piece of filter floss in there for weeks at a time, I have no doubt all the detritus caught in it would break down and go right back into my water in the form of sky-high nutrients.

Bottom line: I’m sold on the benefits of using filter floss.

The type I’ve decide to try is the floss made by InTank. It’s reasonable priced. It’s thicker than many other poly filters that are available. It has great reviews on many aquarium forums. And it has great reviews on as well.

If you decide to give it try, here are a couple of tips for using it…

  • Change it often! I change mine every week when I do my water change. If your tank is really clean you might be able to stretch it to every other week. And if you have a heavy bioload or feed your tank heavily, twice a week would be better.
  • If you cut the sheet down into smaller pieces like I do, I suggest rinsing the pieces after you cut them. It isn’t 100% necessary. But you may see a few small loose fibers floating around in your tank until the new piece of floss has a chance to re-capture them.
  • Position it so that the water enters through the white side and exits through the blue.

If you would like to pick up some InTank filter floss for yourself, you can get it on